U.S. patent number 5,102,597 [Application Number 07/705,451] was granted by the patent office on 1992-04-07 for porous, absorbent, polymeric macrostructures and methods of making the same.
This patent grant is currently assigned to The Procter & Gamble Company. Invention is credited to Charles J. Berg, Frank H. Lahrman, Donald C. Roe.
United States Patent |
5,102,597 |
Roe , et al. |
April 7, 1992 |
Porous, absorbent, polymeric macrostructures and methods of making
the same
Abstract
Absorbent polymeric macrostructures that are porous and comprise
an interparticle crosslinked aggregate having a circumscribed dry
volume greater than about 10.0 mm.sup.3. The interparticle
crosslinked aggregate comprises a multiplicity of precursor
particles of substantially water-insoluble, absorbent,
hydrogel-forming, polymer material; and an interparticle
crosslinking agent reacted with the polymer material of the
precursor particles to form crosslink bonds between the precursor
particles. Because of the particulate nature of the precursor
particles, the macrostructure has pores between adjacent precursor
particles. The pores are interconnected by intercommunicating
channels such that the macrostructure is liquid permeable.
Inventors: |
Roe; Donald C. (Cincinnati,
OH), Lahrman; Frank H. (Cincinnati, OH), Berg; Charles
J. (Cincinnati, OH) |
Assignee: |
The Procter & Gamble
Company (Cincinnati, OH)
|
Family
ID: |
24001904 |
Appl.
No.: |
07/705,451 |
Filed: |
May 24, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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503393 |
Apr 2, 1990 |
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Current U.S.
Class: |
264/126; 521/88;
521/95; 521/149; 521/94; 521/142; 521/919; 521/84.1 |
Current CPC
Class: |
A61F
13/15626 (20130101); A61L 15/425 (20130101); C08J
9/28 (20130101); A61L 15/60 (20130101); B32B
7/02 (20130101); A61F 13/537 (20130101); A61F
2013/530569 (20130101); Y10S 521/919 (20130101); A61F
13/51 (20130101); Y10T 428/234 (20150115); B32B
2305/026 (20130101); Y10T 428/249964 (20150401); A61F
2013/530598 (20130101); A61F 2013/530766 (20130101); A61F
2013/49076 (20130101); A61F 2013/8491 (20130101); A61F
2013/51409 (20130101); Y10T 428/239 (20150115); A61F
13/534 (20130101); A61F 2013/5307 (20130101); Y10T
428/249986 (20150401); C08J 2201/05 (20130101); A61F
2013/530007 (20130101); A61F 2013/530642 (20130101); A61F
2013/49031 (20130101); C08J 2207/12 (20130101); A61F
2013/530708 (20130101); B32B 2307/7265 (20130101); B32B
2307/726 (20130101) |
Current International
Class: |
A61F
13/15 (20060101); A61L 15/42 (20060101); A61L
15/60 (20060101); A61L 15/16 (20060101); B32B
7/02 (20060101); C08J 9/00 (20060101); C08J
9/28 (20060101); B27J 005/00 () |
Field of
Search: |
;264/126
;521/84.1,88,94,95,142,149,919 |
References Cited
[Referenced By]
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GB |
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Other References
Technical Bulletin, Starchem GmbH, Drystar, Publication--date
unknown. .
Kolon Petrochemical Super Absorbent Material. .
Norsolar Absorbent Gelling Material. .
Nippon Shokubai Water Agglomerated Absorbent Gelling
Material..
|
Primary Examiner: Foelak; Morton
Attorney, Agent or Firm: Miller; Steven W. Witte; Richard
C.
Parent Case Text
This is a division of application Ser. No. 503,393, filed on Apr.
2, 1990.
Claims
What is claimed is:
1. A method for producing a porous, absorbent, polymeric
macrostructure comprising an interparticle crosslinked aggregate
having pores interconnected by intercommunicating channels so that
the macrostructure is liquid permeable, the method comprising the
steps of:
(a) providing a multiplicity of precursor particles of
substantially water-insoluble, absorbent, hydrogel-forming, polymer
material;
(b) applying an interparticle crosslinking agent onto said
precursor particles, said interparticle crosslinking agent being
capable of reacting with said polymer material of said precursor
particles;
(c) physically associating said precursor particles to form an
aggregate having pores interconnected by intercommunicating
channels; and
(d) reacting said interparticle crosslinking agent with said
polymer material of said precursor particles of said aggregate,
while maintaining the physical association of said precursor
particles, to form crosslink bonds between said precursor particles
to form an interparticle crosslinked aggregate macrostructure.
2. The method of claim 1 additionally comprising the step of
surface crosslinking the macrostructure.
3. The method of claim 1 additionally comprising the step of
shaping the aggregate to a desired shape, size, and/or density
prior to step (d).
4. The method of claim 1 wherein step (d) comprises heating.
5. The method of claim 1 additionally comprising the step of adding
reinforcing fibers to said precursor particles.
6. The method of claim 1 wherein said interparticle crosslinking
agent comprises a monomer that is polymerized to form polymeric
crosslink bonds between said precursor particles.
7. The method of claim 6 wherein step (d) comprises the step of
initiating the polymerization reaction by irradiating said
monomer.
8. The method of claim 1 wherein said precursor particles have a
mass average particle size less than about 500 microns.
9. The method of claim 1 wherein said precursor particles have a
mass average particle size less than about 300 microns.
10. The method of claim 1 wherein said precursor particles comprise
fibers.
11. A method for producing a porous, absorbent, polymeric
macrostructure comprising an interparticle crosslinked aggregate
having pores interconnected by intercommunicating channels so that
the macrostructure is liquid permeable, the method comprising the
steps of:
(a) providing a multiplicity of substantially dry precursor
particles of substantially water-insoluble, absorbent,
hydrogel-forming, polymer material, said polymer material of said
precursor particles being selected from the group consisting of
hydrolyzed starch-acrylonitrile graft copolymer; partially
neutralized starch-acrylonitrile graft copolymer; starch-acrylic
acid graft copolymer; partially neutralized starch-acrylic acid
graft copolymer; saponified vinyl acetate-acrylic ester copolymers;
hydrolyzed acrylonitrile or acrylamide copolymers; slightly network
crosslinked products of any of the foregoing copolymers; partially
neutralized polyacrylic acid; or slightly network crosslinked
products of partially neutralized polyacrylic acid;
(b) applying an interparticle crosslinking agent onto said
precursor particles, said interparticle crosslinking agent being
selected from the group consisting of polyhydric alcohol compounds,
polyglycidyl ether compounds, polyfunctional aziridine compounds,
polyfunctional amine compounds, and polyfunctional isocyanate
compounds;
(c) physically associating said precursor particles to form an
aggregate having pores interconnected by intercommunicating
channels;
(d) shaping the aggregate to a desired shape, size, and/or density;
and
(e) subsequently heating said interparticle crosslinking agent and
said aggregate to react said interparticle crosslinking agent with
said polymer material of said precursor particles of said
aggregate, while maintaining the physical association of said
precursor particles, to form crosslink bonds between said precursor
particles to form an interparticle crosslinked aggregate
macrostructure.
12. The method of claim 11 additionally comprising the step of
adding fibers to said precursor particles prior to reacting said
interparticle crosslinking agent with said polymer material of said
precursor particles.
13. The method of claim 11 additionally comprising the step of
surface crosslinking the macrostructure.
14. The method of claim 11 wherein said precursor particles
comprise fibers.
15. The method of claim 11 wherein said interparticle crosslinking
agent is mixed with water, an organic solvent, or mixtures
thereof.
16. The method of claim 15 wherein step (d) comprises molding the
aggregate.
17. The method of claim 15 wherein step (d) comprises forming the
aggregate.
18. The method of claim 17 wherein step (d) comprises extruding
said aggregate and subsequently rolling said aggregate to form a
sheet.
19. The method of claim 11 wherein said interparticle crosslinking
agent is selected from the group consisting of trimethylol propane,
ethylene glycol, 1,2-propanediol, 1,3-propanediol, or glycerol; and
said polymer material consists essentially of slightly network
crosslinked products of partially neutralized polyacrylic acid.
20. The method of claim 19 wherein step (e) is carried out at a
temperature in the range of from about 170.degree. C. to about
220.degree. C. for between about 3 hours and about 30 minutes.
21. The method of claim 20 wherein said interparticle crosslinking
agent is mixed with water, an organic solvent, or mixtures
thereof.
22. The method of claim 21 wherein step (d) comprises the steps of
extruding the aggregate and then rolling said aggregate to form a
sheet.
23. The method of claim 22 wherein step (b) comprises atomizing
said interparticle crosslinking agent onto said precursor
particles.
24. The method of claim 22 wherein the mass average particle size
of said precursor particles is less than about 300 microns.
25. The method of claim 24 wherein at least about 95% by weight of
said precursor particles have a particle size between about 150
microns and about 300 microns.
26. The method of claim 22 wherein the mass average particle size
of said precursor particles is less than about 180 microns; and at
least about 95% by weight of said precursor particles have a
particle size between about 90 microns and about 180 microns.
27. The method of claim 19, 24, 25, or 26 additionally comprising
the step of surface crosslinking said precursor particles of said
macrostructure simultaneously with step (e).
28. The method of claim 14, 19, 21, or 24 additionally comprising
the step of adding reinforcing fibers to said precursor particles
prior to reacting said polymer material of said precursor particles
with said interparticle crosslinking agent.
Description
FIELD OF THE INVENTION
The present invention relates to absorbent polymeric compositions
which, upon contacting liquids such as water or body exudates,
swell and imbibe such liquids. More specifically, the present
invention relates to polymeric compositions that are
macrostructures such as a sheet, film, or strip. Such absorbent
polymeric macrostructures are porous so as to be liquid permeable.
These porous, absorbent, polymeric macrostructures are useful by
themselves or in absorbent articles such as diapers, adult
incontinence pads, sanitary napkins, and the like. The present
invention also relates to methods of producing such porous,
absorbent, polymeric macrostructures.
BACKGROUND OF THE INVENTION
Particulate, absorbent, polymeric compositions are capable of
absorbing large quantities of liquids such as water and body
exudates and which are further capable of retaining such absorbed
liquids under moderate pressures. These absorption characteristics
of such polymeric compositions make them especially useful for
incorporation into absorbent articles such as diapers. For example,
U.S. Pat. No. 3,699,103 issued to Harper et al. on June 13, 1972
and U.S. Pat. 3,670,731 issued to Harmon on June 20, 1972, both
disclose the use of particulate, absorbent, polymeric compositions
(also referred to as hydrogels, superabsorbent, or hydrocolloid
materials) in absorbent articles.
Conventional particulate, absorbent, polymeric compositions,
however, have the limitation that the particles are not immobilized
and are free to migrate during processing and/or use. Migration of
the particles during processing can lead to material handling
losses during manufacturing operations as well as nonhomogeneous
incorporation of the particles into structures in which the
particles are being used. A more significant problem, though,
occurs when these particulate materials migrate during or after
swelling. Such mobility leads to high resistance to liquid flow
through the material due to the lack of stable interparticle
capillary or liquid transport channels. This phenomenon is one form
of what is commonly referred to as "gel blocking".
One attempt to overcome the performance limitations associated with
particle mobility in the context of their use in absorbent articles
has been the incorporation of the particulate, absorbent, polymeric
compositions into tissue laminates (layered absorbent members). By
encapsulating the particles between tissue layers, the overall
particle mobility within an absorbent member is diminished.
However, upon liquid contact, the particles within the laminate are
often free to move relative to each other resulting in the
breakdown of any preexistent interparticle capillary channels.
Another attempted solution has been to immobilize the particulate,
absorbent, polymeric compositions by the addition of large
quantities of liquid polyhydroxy compounds that act as an adhesive
to hold the particles together or to a substrate. An example of
this technology is disclosed in U.S. Pat. No. 4,410,571 issued to
Korpman on Oct. 18, 1983. While this approach does limit migration
before and, to some extent, during swelling, the particles
eventually become detached from each other upon presentation of
excess liquid to such polymeric compositions, resulting again in
the breakdown of any preexisting capillary channels between the
particles.
A further attempt to overcome the problem has been to produce a
superabsorbent film via extrusion of a solution of a linear polymer
and subsequent crosslinking of the polymer. An example of this
technology is disclosed in U.S. Pat. No. 4,861,539 issued to Allen
et al. on Aug. 29, 1989. While these superabsorbent films may
absorb significant quantities of liquids, they have limited liquid
transport properties and are prone to gel blocking due to their
lack of internal capillary channels.
Therefore, the present invention seeks to resolve the above
problems by providing a porous, absorbent, polymeric
macrostructure.
Thus, it is an object of the present invention to provide absorbent
polymeric macrostructures that are porous.
It is a further object of the present invention to provide
absorbent polymeric macrostructures that remain intact and
transport liquid even upon saturation with excess liquid.
It is a still further object of the present invention to provide
absorbent polymeric macrostructures wherein the component precursor
particles and pores retain their relative geometry and spatial
relationships even upon saturation with excess liquid.
It is an even further object of the present invention to provide
absorbent polymeric macrostructures that increase in liquid
permeability upon swelling.
It is another object of the present invention to provide a method
for producing such absorbent polymeric macrostructures.
It a further object of the present invention to provide improved
absorbent products, absorbent members, and absorbent articles (such
as diapers or sanitary napkins) incorporating the absorbent
polymeric macrostructures of the present invention.
SUMMARY OF THE INVENTION
The present invention provides an absorbent polymeric
macrostructure that is porous. The porous, absorbent, polymeric
macrostructure comprises an interparticle crosslinked aggregate
having a circumscribed dry volume greater than about 10.0 mm.sup.3.
The interparticle crosslinked aggregate comprises a multiplicity of
precursor particles of substantially water-insoluble, absorbent,
hydrogel-forming, polymer material; and an interparticle
crosslinking agent reacted with the polymer material of the
precursor particles to form crosslink bonds between different
precursor particles. Because of the particulate nature of the
precursor particles, the macrostructure has pores between adjacent
precursor particles. The pores are interconnected by
intercommunicating channels such that the macrostructure is liquid
permeable (i.e., has capillary transport channels).
Due to the interparticle crosslink bonds formed between the
precursor particles forming the interparticle crosslinked
aggregate, the resultant macrostructure has improved structural
integrity, increased liquid acquisition and distribution rates, and
minimal gel blocking characteristics. It has been found that when
the macrostructure is contacted with liquids, the macrostructure
swells generally isotropically even under moderate confining
pressures, imbibes such liquids into the precursor particles, and
absorbs such liquids into the pores. The isotropic swelling of the
macrostructure allows the precursor particles and the pores to
maintain their relative geometry and spatial relationships even
when swollen. Thus, the macrostructures are relatively "fluid
stable" in that the precursor particles do not dissociate from each
other, thereby minimizing the incidence of gel blocking and
allowing the capillary channels to be maintained and enlarged when
swollen so that the macrostructure may acquire and transport
subsequent loadings of liquid, even excess liquid.
The present invention also relates to improved absorbent products,
absorbent members, and absorbent articles incorporating the porous,
absorbent, polymeric macrostructures of the present invention. The
macrostructures enhance the liquid handling characteristics of such
products by rapidly acquiring liquids, efficiently distributing and
storing such liquids, allowing for the acquisition and transport of
subsequent loadings of liquids, and minimizing gel blocking and gel
migration within such products.
The present invention also relates to methods of producing such
porous, absorbent, polymeric macrostructures. The macrostructures
are produced by applying an interparticle crosslinking agent onto
the precursor particles, physically associating the precursor
particles into an aggregate, and reacting the interparticle
crosslinking agent with the polymer material of the precursor
particles to form crosslink bonds between different precursor
particles. In a preferred embodiment, the macrostructures are
produced by shaping the aggregate of the associated precursor
particles to form macrostructures of a desired shape, size, and/or
density. The component precursor particles of the macrostructures
may also be surface crosslinked.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing
out and distinctly claiming the present invention, it is believed
the present invention will be better understood from the following
description in conjunction with the accompanying drawings in
which:
FIG. 1 is a photomicrograph enlarged approximately 40 times showing
a perspective view (at 15.degree. from the horizontal) of the edge
of a porous, absorbent, polymeric macrostructure of the present
invention;
FIG. 2 is a photomicrograph enlarged approximately 120 times of a
top view of a portion of the macrostructure shown in FIG. 1;
FIG. 3 is a photomicrograph enlarged approximately 30 times showing
a perspective view (at 45.degree. from the horizontal) of the
corner of the macrostructure shown in FIG. 1;
FIG. 4 is a photomicrograph enlarged approximately 20 times of a
top view of a portion of an alternative embodiment of a porous,
absorbent, polymeric macrostructure having superabsorbent fibers
used in the macrostructure;
FIG. 5 is a photomicrograph enlarged approximately 50 times of a
top view of a portion of the macrostructure of FIG. 4;
FIG. 6 is a photomicrograph enlarged approximately 75 times of a
top view of a portion of the macrostructure of FIG. 4;
FIG. 7 is a photomicrograph enlarged approximately 100 times of a
perspective view (45.degree. from the horizontal) of a portion of
an alternative embodiment of a porous, absorbent, polymeric
macrostructure having polyester fibers embedded in the
macrostructure;
FIG. 8 is a perspective view of a disposable diaper embodiment of
the present invention wherein portions of the topsheet have been
cut-away to more clearly show the underlying absorbent core (an
embodiment of an absorbent member of the present invention) of the
diaper wherein the absorbent member comprises a porous, absorbent,
polymeric macrostructure of the present invention;
FIG. 9 is a cross-sectional view of the absorbent core of the
diaper shown in FIG. 8 taken along sectional line 9--9 of FIG. 8;
and
FIG. 10 is a perspective view of a disposable diaper embodiment of
the present invention wherein portions of the topsheet have been
cut away to more clearly show an alternative absorbent core
embodiment.
DETAILED DESCRIPTION OF THE INVENTION
Porous, absorbent, polymeric macrostructures of the present
invention are structures capable of absorbing large quantities of
liquids such as water and/or body exudates (e.g., urine or menses)
and which are capable of retaining such liquids under moderate
pressures. Typically, the porous, absorbent, polymeric
macrostructures of the present invention will swell generally
isotropically and rapidly absorb the liquids.
As used herein, the term "macrostructure" means a product having a
circumscribed volume when substantially dry (i.e., circumscribed
dry volume) of at least about 10.0 mm.sup.3, preferably at least
about 100 mm.sup.3, more preferably at least about 500 mm.sup.3.
Typically, the macrostructures of the present invention will have a
circumscribed dry volume much greater than about 500 mm.sup.3. In
preferred embodiments of the present invention, the macrostructures
have a circumscribed dry volume of between about 1000 mm.sup.3 and
about 100,000 mm.sup.3.
While the macrostructures of the present invention may have a
number of shapes and sizes, the macrostructures are typically in
the form of sheets, films, cylinders, blocks, spheres, fibers,
filaments, or other shaped elements. The macrostructures will
generally have a thickness or diameter between about 0.25 mm and
about 10.0 mm. Preferably for use in absorbent products, the
macrostructures are in the form of a sheet. The term "sheet" as
used herein describes macrostructures having a thickness greater
than about 250 microns. The sheets will preferably have a thickness
between about 0.5 mm and about 3 mm, typically about 1 mm.
The macrostructures of the present invention are formed from
polymer materials capable of absorbing large quantities of liquids.
(Such polymer materials are commonly referred to as hydrogel,
hydrocolloid, or superabsorbent materials.) The macrostructures
preferably comprise substantially water-insoluble, absorbent,
hydrogel-forming, polymer material. The specific polymer materials
will be discussed herein with respect to the polymer materials
forming the precursor particles.
As shown in FIGS. 1 and 3, the porous, absorbent, polymeric
macrostructures of the present invention comprise an interparticle
crosslinked aggregate. An interparticle crosslinked aggregate is
the porous structure formed by joining together two or more,
typically about ten or more in the present invention, previously
independent precursor particles. The precursor particles are joined
together by interparticle crosslinking agents applied thereto and
subjected to conditions, while maintaining the physical association
of the precursor particles, which are sufficient to react the
interparticle crosslinking agent with the polymer material of the
precursor particles to form crosslink bonds between the precursor
particles that form the aggregate.
As shown in FIG. 1, the interparticle crosslinked aggregate is
formed from a multiplicity of precursor particles. Due to the
preferred size for the precursor particles used herein, the
interparticle crosslinked aggregate is typically formed from ten or
more, preferably about fifty or more, precursor particles. The
precursor particles of the present invention are in the form of
discrete units. The precursor particles can comprise granules,
pulverulents, spheres, flakes, fibers, aggregates or agglomerates.
Thus, the precursor particles can have any desired shape such as
cubic; rod-like; polyhedral; spherical; rounded; angular;
irregular; randomly-sized irregular shapes (e.g., pulverulent
products of a grinding or pulverizing step) or shapes having a
large greatest dimension/smallest dimension ratio like needle-like,
flake-like, or fibrous shapes, and the like. Preferably, as shown
in FIGS. 1-3, the precursor particles are in a finely divided
powder form of randomly-sized irregular shaped pulverulent granules
or flakes.
Although the precursor particles may have a size varying over a
wide range, specific particle size distributions and sizes are
preferred. For purposes of the present invention, particle size is
defined for precursor particles that do not have a large greatest
dimension/smallest dimension ratio such as fibers (e.g., granules,
flakes, or pulverulents) as the dimension of a precursor particle
which is determined by sieve size analysis. Thus, for example, a
precursor particle that is retained on a standard #30 sieve with
600 micron openings is considered to have a particle size greater
than 600 microns, a precursor particle that passes through the #30
sieve with 600 micron openings and is retained on a standard #35
sieve with 500 micron openings is considered to have a particle
size between 500 and 600 microns, and a precursor particle that
passes through a #35 sieve with 500 micron openings is considered
to have a particle size less than 500 microns. In preferred
embodiments of the present invention, the precursor particles will
generally range in size from between about 1 micron to about 2000
microns, more preferably between about 20 microns to about 1000
microns.
Further, for purposes of this invention, the mass average particle
size of the precursor particles is important in determining the
characteristics and properties of the resultant macrostructures.
The mass average particle size of a given sample of precursor
particles is defined as the particle size which is the average
particle size of the sample on a mass basis. A method for
determining the mass average particle size of a sample is described
hereinafter in the Test Methods section. The mass average particle
size of the precursor particles will generally be from about 20
microns to about 1500 microns, more preferably from about 50
microns to about 1000 microns. In preferred embodiments of the
present invention, the precursor particles have a mass average
particle size less that about 1000 microns, more preferably less
than about 600 microns, most preferably less than about 500 microns
In especially preferred embodiments of the present invention, the
mass average particle size of the precursor particles is relatively
small (i.e., the precursor particles are fines). In these
embodiments, the mass average particle size of the precursor
particles is less than about 300 microns, more preferably less than
about 180 microns. In an exemplary embodiment, at least about 95%
by weight of the precursor particles have a particle size between
about 150 microns and about 300 microns. In an alternative
embodiment, at least about 95% by weight of the precursor particles
have a particle size between about 90 microns and about 180
microns. Narrow precursor particle size distributions are preferred
because they result in a higher porosity macrostructure due to
their higher void fraction when densified versus broader precursor
particle size distributions with equivalent mass average particle
sizes.
The particle size of materials having a large greatest
dimension/smallest dimension such as fibers is typically defined by
their largest dimension. For example, if absorbent, polymeric
fibers (i.e., superabsorbent fibers) are used in the
macrostructures of the present invention, the length of the fibers
is used to define the "particle size". (The denier and/or the
diameter of the fibers may also be specified.) In exemplary
embodiments of the present invention, the fibers have a length
greater than about 5 mm, preferably between about 10 mm and about
100 mm, more preferably between about 10 mm and about 50 mm.
The precursor particles comprise substantially water-insoluble,
absorbent, hydrogel-forming, polymer material. Examples of polymer
materials suitable for use as the precursor particles herein
include those which are prepared from polymerizable, unsaturated,
acid-containing monomers. Thus, such monomers include the
olefinically unsaturated acids and anhydrides which contain at
least one carbon to carbon olefinic double bond. More specifically,
these monomers can be selected from olefinically unsaturated
carboxylic acids and acid anhydrides, olefinically unsaturated
sulfonic acids and mixtures thereof
Some non-acid monomers may also be used to prepare the precursor
particles herein. Such non-acid monomers can include, for example,
the water-soluble or water-dispersible esters of the
acid-containing monomers as well as monomers which contain no
carboxyl or sulfonic acid groups at all. Optional non-acid monomers
can thus include monomers containing the following types of
functional groups: carboxylic acid or sulfonic acid esters,
hydroxyl groups, amide-groups, amino groups, nitrile groups and
quaternary ammonium salt groups. These non-acid monomers are well
known materials and are described in greater detail, for example,
in U.S. Pat. No. 4,076,663 issued to Masuda et al. on Feb. 28, 1978
and in U.S. Pat. No. 4,062,817 issued to Westerman on Dec. 13,
1977, both of which are incorporated herein by reference.
Olefinically unsaturated carboxylic acid and carboxylic acid
anhydride monomers include the acrylic acids typified by acrylic
acid itself, methacrylic acid, ethacrylic acid, alpha-chloroacrylic
acid, alpha-cyano acrylic acid, beta-methyl acrylic acid (crotonic
acid), alpha-phenyl acrylic acid, beta-acryloxy propionic acid,
sorbic acid, alpha-chloro sorbic acid, angelic acid, cinnamic acid,
p-chloro cinnamic acid, beta-steryl acrylic acid, itaconic acid,
citraconic acid, mesaconic acid, glutaconic acid, aconitic acid,
maleic acid, fumaric acid, tricarboxyethylene and maleic acid
anhydride.
Olefinically unsaturated sulfonic acid monomers include aliphatic
or aromatic vinyl sulfonic acids such as vinylsulfonic acid, allyl
sulfonic acid, vinyltoluene sulfonic acid and styrene sulfonic
acid; acrylic and methacrylic sulfonic acid such as sulfoethyl
acrylate, sulfoethyl methacrylate, sulfopropyl acrylate,
sulfopropyl methacrylate, 2-hydroxy-3-acryloxy propyl sulfonic
acid, 2-hydroxy-3-methacryloxy propyl sulfonic acid and
2-acrylamido-2-methyl propane sulfonic acid.
Preferred polymer materials for use in the present invention
possess a carboxyl group. These polymers include hydrolyzed
starch-acrylonitrile graft copolymer, partially neutralized
starch-acrylonitrile graft copolymer, starch-acrylic acid graft
copolymer, partially neutralized starch-acrylic acid graft
copolymer, saponified vinyl acetate-acrylic ester copolymers,
hydrolyzed acrylonitrile or acrylamide copolymers, slightly network
crosslinked products of any of the foregoing copolymers, partially
neutralized polyacrylic acid, and slightly network crosslinked
products of partially neutralized polyacrylic acid. These polymers
may be used either independently or in the form of a mixture of two
or more monomers, compounds, or the like. Examples of these polymer
materials are disclosed in U.S. Pat. Nos. 3,661,875; 4,076,663;
4,093,776; 4,666,983; and 4,734,478.
Most preferred polymer materials for use as the precursor particles
are slightly network crosslinked products of partially neutralized
polyacrylic acids and starch derivatives therefrom. Most
preferably, the precursor particles comprise from about 50 to about
95%, preferably about 75% , neutralized, slightly network
crosslinked, polyacrylic acid (i.e., poly (sodium acrylate/acrylic
acid)).
As described above, the precursor particles preferably are polymer
materials that are slightly network crosslinked. Network
crosslinking serves to render the precursor particles substantially
water-insoluble and in part serves to determine the absorptive
capacity and extractable polymer content characteristics of the
precursor particles and the resultant macrostructure. Processes for
network crosslinking the polymers and typical network crosslinking
agents are described in greater detail in the
hereinbefore-referenced U.S. Pat. No. 4,076,663.
The individual precursor particles may be formed in any
conventional manner. Typical and preferred processes for producing
the individual precursor particles are described in: U.S. Pat. No.
Re. 32,649 entitled "Hydrogel-Forming Polymer Compositions For Use
In Absorbent Structures" reissued to Kerryn A. Brandt, Steven A.
Goldman, and Thomas A. Inglin on Apr. 19, 1988; U.S. Pat. No.
4,666,983 entitled "Absorbent Article" issued to Tsuneo
Tsubakimoto, Tadao Shimomura, and Yoshio Irie on May 19, 1987; and
U.S. Pat. No. 4,625,001 entitled "Method For Continuous Production
Of Cross-Linked Polymer" issued to Tsuneo Tsubakimoto, Tadao
Shimomura, and Yoshio Irie on Nov. 25, 1986. These patents are
incorporated herein by reference.
Preferred methods for forming the precursor particles are those
that involve aqueous solution or other solution polymerization
methods. As described in the above-referenced U.S. Pat. No. Re.
32,649, aqueous solution polymerization involves the use of an
aqueous reaction mixture to carry out polymerization to form the
precursor particles. The aqueous reaction mixture is then subjected
to polymerization conditions which are sufficient to produce in the
mixture, substantially water-insoluble, slightly network
crosslinked polymer material. The mass of polymer material thereby
formed is then pulverized or chopped to form the individual
precursor particles.
More specifically, the aqueous solution polymerization method for
producing the individual precursor particles comprises the
preparation of an aqueous reaction mixture in which to carry out
polymerization to form the desired precursor particles. One element
of such a reaction mixture is the acid group-containing monomer
material which will form the "backbone" of the precursor particles
to be produced. The reaction mixture will generally comprise about
100 parts by weight of the monomer material. Another component of
the aqueous reaction mixture comprises a network crosslinking
agent. Network crosslinking agents useful in forming the precursor
particles are described in more detail in the above-referenced U.S.
Pat. No. Re. 32,649 issued to Brandt et al.; U.S. Pat. No.
4,666,983 issued to Tsubakimoto et al.; and U.S. Pat. No. 4,625,001
issued to Tsubakimoto et al.. The network crosslinking agent will
generally be present in the aqueous reaction mixture in an amount
of from about 0.001 mole percent to about 5 mole percent based on
the total moles of monomer present in the aqueous mixture (about
0.01 to about 20 parts by weight, based on 100 parts by weight of
the monomer material). An optional component of the aqueous
reaction mixture comprises a free radical initiator including, for
example, peroxygen compounds such as sodium, potassium, and
ammonium persulfates, caprylyl peroxide, benzoyl peroxide, hydrogen
peroxide, cumene hydroperoxides, tertiary butyl diperphthalate,
tertiary butyl perbenzoate, sodium peracetate, sodium percarbonate,
and the like. Other optional components of the aqueous reaction
mixture comprise the various non-acidic co-monomer materials
including esters of the essential unsaturated acidic functional
group-containing monomers or other co-monomers containing no
carboxyl or sulfonic acid functionalities at all.
The aqueous reaction mixture is subjected to polymerization
conditions which are sufficient to produce in the mixture
substantially water-insoluble, absorbent, hydrogel-forming,
slightly network crosslinked polymer materials. The polymerization
conditions are also discussed in more detail in the three
above-referenced patents. Such polymerization conditions generally
involve heating (thermal activation techniques) to a polymerization
temperature from about 0.degree. C. to about 100.degree. C., more
preferably from about 5.degree. C. to about 40.degree. C.
Polymerization conditions under which the aqueous reaction mixture
is maintained can also include, for example, subjecting the
reaction mixture, or portions thereof, to any conventional form of
polymerization activating irradiation. Radioactive, electronic,
ultraviolet, or electromagnetic radiation are alternative
conventional polymerization techniques.
The acid functional groups of the polymer materials formed in the
aqueous reaction mixture are also preferably neutralized.
Neutralization can be carried out in any conventional manner which
results in at least about 25 mole percent, and more preferably at
least about 50 mole percent, of the total monomer utilized to form
the polymer material being acid group-containing monomers that are
neutralized with a salt-forming cation. Such salt-forming cations
include, for example, alkali metals, ammonium, substituted ammonium
and amines as discussed in further detail in the above-referenced
U.S. Pat. No. Re. 32,649 issued to Brandt et al.
While it is preferred that the precursor particles be manufactured
using an aqueous solution polymerization process, it is also
possible to carry out the polymerization process using multi-phase
polymerization processing techniques such as inverse emulsion
polymerization or inverse suspension polymerization procedures. In
the inverse emulsion polymerization or inverse suspension
polymerization procedures, the aqueous reaction mixture as
hereinbefore described is suspended in the form of tiny droplets in
a matrix of a water-immiscible, inert organic solvent such as
cyclohexane. The resultant precursor particles are generally
spherical in shape. Inverse suspension polymerization procedures
are described in greater detail in U.S. Pat. No. 4,340,706 issued
to Obaysashi et al. on July 20, 1982; U.S. Pat. No. 4,506,052
issued to Flesher et al. on Mar. 19, 1985; and U.S. Pat. No.
4,735,987 issued to Morita et al. on Apr. 5, 1988; each of these
patents being incorporated herein by reference.
In preferred embodiments of the present invention, the precursor
particles used to form the interparticle crosslinked aggregate are
substantially dry. The term "substantially dry" is used herein to
mean that the precursor particles have a liquid content, typically
water or other solution content, less than about 50%, preferably
less than about 20%, more preferably less than about 10%, by weight
of the precursor particles. In general, the liquid content of the
precursor particles is in the range of from about 0.01% to about 5%
by weight of the precursor particles. The individual precursor
particles can be dried by any conventional method such as by
heating. Alternatively, when the precursor particles are formed
using an aqueous reaction mixture, water can be removed from the
reaction mixture by azeotropic distillation. The polymer-containing
aqueous reaction mixture can also be treated with a dewatering
solvent such as methanol. Combinations of these drying procedures
may also be used. The dewatered mass of polymer material can then
be chopped or pulverized to form substantially dry precursor
particles of substantially water-insoluble, absorbent,
hydrogel-forming, polymer material.
Preferred precursor particles of the present invention are those
which exhibit a high absorptive capacity so that the resultant
macrostructure formed from such precursor particles also has a high
absorptive capacity. Absorptive capacity refers to the capacity of
a given polymer material to absorb liquids with which it comes into
contact. Absorptive capacity can vary significantly with the nature
of the liquid being absorbed and with the manner in which the
liquid contacts the polymer material. For purposes of this
invention, Absorptive Capacity is defined in terms of the amount of
Synthetic Urine (as hereinafter defined) absorbed by any given
polymer material in terms of grams of Synthetic Urine per gram of
polymer material in a procedure hereinafter defined in the Test
Methods section. Preferred precursor particles of the present
invention are those which have an Absorptive Capacity of at least
about 20 grams, more preferably at least about 25 grams, of
Synthetic Urine per gram of polymer material. Typically, the
polymer materials of the precursor particles herein have an
Absorptive Capacity of from about 40 grams to about 70 grams of
Synthetic Urine per gram of polymer material. Precursor particles
having this relatively high absorptive capacity characteristic
produce macrostructures that are especially useful in absorbent
products, absorbent members, and absorbent articles since the
resultant macrostructures formed from such precursor particles can,
by definition, hold desirably high amounts of discharged body
exudates such as urine.
The individual precursor particles may optionally be surface
treated. For example, U.S. Pat. No. 4,824,901 issued to Alexander
et al. on Apr. 25, 1989, discloses the surface treatment of
polymeric particles with a poly-quaternary amine. If surface
treated, the precursor particles are preferably surface crosslinked
as disclosed in U.S. Pat. No. 4,666,983, entitled "Absorbent
Article", issued to Tsubakimoto et al. on May 19, 1987; and U.S.
Pat. No. 4,734,478, entitled "Water Absorbing Agent" issued to
Tsubakimoto et al. on Mar. 29, 1988; which patents are incorporated
herein by reference. As disclosed in the Tsubakimoto et al. '983
patent, the individual precursor particles may be surface
crosslinked by applying a surface crosslinking agent onto the
precursor particles and reacting the surface crosslinking agent
with the polymer material on the surface of the precursor
particles.
While all of the precursor particles of the interparticle
crosslinked aggregate are preferably formed of the same polymer
material with the same properties, this need not be the case. For
example, some precursor particles may comprise a polymer material
of a starch-acrylic acid graft copolymer while other precursor
particles may comprise a polymer material of slightly network
crosslinked products of partially neutralized polyacrylic acid.
Further, the precursor particles of the interparticle crosslinked
aggregate may vary in shape, absorptive capacity, or any other
property or characteristic of the precursor particles. In a
preferred embodiment of the present invention, the precursor
particles comprise a polymer material consisting essentially of
slightly network crosslinked products of partially neutralized
polyacrylic acid; each precursor particle having similar
properties.
The interparticle crosslinked aggregate of the present invention
also comprises an interparticle crosslinking agent. The
interparticle crosslinking agent is applied onto the precursor
particles and reacted with the polymer material of the precursor
particles while physical association between the precursor
particles is maintained. This reaction forms crosslink bonds
between the precursor particles. Thus, the crosslink bonds are
interparticle in nature (i.e., between different precursor
particles). Without wishing to be bound by theory or limit the
scope of the invention, it is believed the reaction of the
interparticle crosslinking agent with the polymer material of the
precursor particles forms crosslink bonds between the polymer
chains of different precursor particles (i.e., interparticle
crosslink bonds). For the preferred polymers herein, it is believed
the interparticle crosslinking agent reacts to form crosslink bonds
between the carboxyl groups of the previously independent precursor
particles. Without wishing to be bound by theory or limit the scope
of the invention, for the preferred polymer materials possessing
carboxyl groups, it is believed that the interparticle crosslinking
agent reacts with the carboxyl groups of the polymer materials to
form covalent chemical crosslink bonds between the polymer chains
of different precursor particles. The covalent chemical crosslink
bonds generally arise as a result of the formation of ester, amide
(imide) or urethane groups by reaction of the functional groups of
the crosslinking agents with the carboxyl groups of the polymer
material. In preferred executions, it is believed that ester bonds
are formed. Thus, preferred interparticle crosslinking agents are
those agents capable of reacting with the carboxyl groups in the
preferred polymers to form ester bonds.
Interparticle crosslinking agents useful in the present invention
are those that react with the polymer material of the precursor
particles used to form the interparticle crosslinked aggregates.
Suitable interparticle crosslinking agents may comprise a number of
different agents such as, for example, compounds having, at least
two polymerizable double bonds; compounds having at least one
polymerizable double bond and at least one functional group
reactive with the polymer material; compounds having at least two
functional groups reactive with the polymer material; or polyvalent
metal compounds. Specific crosslinking agents useful in the present
invention are described in more detail in the hereinbefore
referenced U.S. Pat. No. 4,076,663 and U.S. Pat. No. Re. 32,649
which are incorporated herein by reference. The interparticle
crosslinking agents may also comprise monomers (such as previously
described) reactive with the polymer material of the precursor
particles to form polymeric crosslink bonds.
Where carboxyl groups are present on or in the polymer material
(i.e., the polymer chains) of the precursor particles, preferred
interparticle crosslinking agents are solutions possessing at least
two functional groups per molecule capable of reacting with the
carboxyl group. Preferred interparticle crosslinking agents include
polyhydric alcohols such as ethylene glycol, diethylene glycol,
triethylene glycol, tetraethylene glycol, polyethylene glycol,
glycerol (1,2,3-propanetriol), polyglycerol, propylene glycol, 1,
2-propanediol, 1, 3-propanediol, trimethylol propane,
diethanolamine, triethanolamine, polyoxypropylene
oxyethylene-oxypropyle block copolymer, sorbitan fatty acid esters,
polyexyethylene sorbitan fatty acid esters, pentaerythritol, and
sorbitol; polyglycidyl ether compounds such as ethylene glycol
diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol
polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol
polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol
polyglycidyl ether, propylene glycol diglycidyl ether, and
propylene glycol diglycidyl ether; polyaziridine compounds such as
2, 2-bishydroxymethyl butanol-tris[3-(i-aziridine) propionate], 1,
6-hexamethyl tolulene diethylene urea, and diphenyl methane-bis-4,
4'-N,N'-diethylene urea; haloepoxy compounds such as
epichlorohydrin and .alpha.-methylfluorohydrin; polyaldehyde
compounds such as glutaraldehyde and glyoxazole, polyamine
compounds such as ethylene diamine, diethylene triamine,
triethylene tetramine, tetraethylene pentamine, pentaethylene
hexamine, and polyethylene imine; and polyisocyanate compounds such
as 2, 4-toluene diisocyanate and hexamethylene diisocyanate.
One interparticle crosslinking agent or two or more substantially
mutually unreactive interparticle crosslinking agents selected from
the group mentioned above may be used. Particularly preferred
interparticle crosslinking agents for use herein with
carboxyl-containing polymer material are ethylene glycol; glycerol;
trimethylol propane; 1, 2-propanediol; and 1, 3-propanediol.
The proportion of the interparticle crosslinking agent to be used
in the present invention is in the range of from about 0.01 parts
to about 30 parts by weight, preferably from about 0.5 parts to
about 10 parts by weight, most preferably from about 1 part to
about 5 parts by weight, per 100 parts by weight of the precursor
particles.
In the present invention, other materials or agents can be used
with the interparticle crosslinking agent(s) as an aid in producing
the interparticle crosslinked aggregate, or in promoting or
assisting in the reaction of the interparticle crosslinking agent
with the polymer material of the precursor particles, or as
associating agents.
For example, water may be used in conjunction with the
interparticle crosslinking agent. The water functions to promote
uniform dispersion of the interparticle crosslinking agent on the
surface of the precursor particles and permeation of the
interparticle crosslinking agent into the surface region of the
precursor particles. The water also promotes stronger physical
association between the precursor particles of the prereacted
aggregates, and the dry and swollen integrity of the resultant
interparticle crosslinked aggregates. In the present invention, the
water is used in a proportion of less than about 20 parts by weight
(0 parts to about 20 parts by weight), preferably in the range of
from about 0.01 parts to about 20 parts by weight, more preferably
in the range of from about 0.1 parts to about 10 parts by weight,
based on 100 parts by weight of the precursor particles. The actual
amount of water to be used will vary depending upon the kind of
polymer material and the particle size of the precursor
particles.
Organic solvents may also be used in conjunction with the
interparticle crosslinking agent. The organic solvents are used to
promote uniform dispersion of the interparticle crosslinking agent
on the surface of the precursor particles. The organic solvents are
preferably hydrophilic organic solvents. The hydrophilic organic
solvents useful in the present invention include lower alcohols
such as methanol, ethanol, n-propanol, isopropanol, n-butanol,
isobutanol, sec-butanol and t-butanol; ketones such as acetone,
methylethyl ketone, and methylisobutyl ketone; ethers such as
dioxane, tetrahydrofuran, and diethyl ether; amides such as N,
N-dimethylformamide and N, N-diethylformamide; and sulfoxides such
as dimethyl sulfoxide. The hydrophilic organic solvent is used in
the present invention in a proportion of less than about 60 parts
by weight (0 parts to about 60 parts by weight), preferably in the
range of from about 0.01 parts to about 60 parts by weight, more
preferably from about 1 part to about 20 parts by weight, based on
100 parts by weight of the precursor particles. The actual amount
of hydrophilic organic solvent to be used will vary depending upon
the kind of polymer material and the particle size of the precursor
particles.
The interparticle crosslinking agent may also be used in a mixture
with water and one or more hydrophilic organic solvents. It has
been found that the use of a water/interparticle crosslinking agent
solution provides the greatest penetration of the crosslinker into
the surface region of the precursor particles while a solution of
hydrophilic organic solvent/interparticle crosslinking agent
provides minimal penetration of the crosslinker. However, a mixture
of all three agents is preferred in order to control the amount of
the penetration of the interparticle crosslinking agent into the
surface region of the precursor particles. Specifically, it has
been found that the higher the water to organic solvent component
ratio, the deeper the crosslinker penetration, the greater the
fluid stability of the macrostructure under stress, and the greater
the reduction in the resultant absorptive capacity of the
macrostructure. Typically, the ratio of water to hydrophilic
organic solvent in the solution will be in the range of from about
10:1 to about 1:10. The hydrophilic organic
solvent/water/interparticle crosslinking agent solution is used in
a proportion less than about 60 parts by weight (0 parts to about
60 parts by weight), preferably in the range of from about 0.01
parts to about 60 parts by weight, more preferably from about 1
part to about 20 parts by weight, based on 100 parts by weight of
the precursor particles.
Other optional components may also be mixed with the solution
containing the interparticle crosslinking agent. For example, an
initiator, a catalyst, or non-acid co-monomer materials may be
added. Examples of these materials suitable for use herein are
described in the hereinbefore referenced U.S. Pat. No. Re.
32,649.
The method of producing the porous, absorbent, polymeric
macrostructure comprising an interparticle crosslinked aggregate
comprises the steps of providing precursor particles of the type
herein described; applying an interparticle crosslinking agent to a
portion of the precursor particles; physically associating the
precursor particles to form an aggregate; shaping the aggregate;
and reacting the interparticle crosslinking agent with the polymer
material of the precursor particles of the aggregate, while
maintaining the physical association of the precursor particles, to
form crosslink bonds between the polymer chains of different
precursor particles.
The interparticle crosslinking agent is applied onto the precursor
particles. The interparticle crosslinking agent may be applied by
any of various techniques and apparatus used for applying solutions
to materials including coating, dumping, pouring, dropping,
spraying, atomizing, condensing, or immersing the interparticle
crosslinking agent onto the precursor particles. As used herein,
the term "applied onto" means that at least a portion of the
surface area of at least one of the precursor particles to be
joined has the interparticle crosslinking agent on it. Thus, the
interparticle crosslinking agent may be applied onto only some of
the precursor particles, onto all of the precursor particles, onto
only a portion of the surface of some or all of the precursor
particles, or onto the entire surface of some or all of the
precursor particles. Preferably, the interparticle crosslinking
agent is coated onto the entire surface of most, preferably all, of
the precursor particles so as to enhance the efficiency, strength,
and density of the interparticle crosslink bonds between the
precursor particles.
In the preferred embodiments of the present invention, after the
interparticle crosslinking agent has been applied onto the
precursor particles, the interparticle crosslinking agent is mixed
with the precursor particles by any of a number of mixing
techniques to insure that the precursor particles are thoroughly
coated with the interparticle crosslinking agent. Because the
precursor particles are thoroughly coated with the interparticle
crosslinking agent, the efficiency, strength, and density of the
crosslink bonds between the precursor particles are enhanced. The
mixing can be accomplished using various techniques and apparatus,
including various mixers or kneaders, as are known in the art.
Before, during, or after applying the interparticle crosslinking
agent onto the precursor particles, the precursor particles are
physically associated together to form an aggregate macrostructure.
The term "physically associated" is used herein to mean that the
precursor particles are brought together and remain in contact with
each other as component parts in any of a number of various ways
and spatial relationships so as to form a single unit (an aggregate
macrostructure).
The precursor particles are preferably physically associated
together by applying an associating agent onto the precursor
particles and physically contacting the precursor particles at at
least the portion of the surface of the precursor particles having
the associating agent applied thereto. Preferred associating agents
cause the polymer material of the precursor particles, when brought
together, to adhere together by the action of fluid surface tension
forces and/or the entanglement of polymer chains due to external
swelling. Associating agents useful in the present invention
include hydrophilic organic solvents, typically low molecular
weight alcohols such as methanol, ethanol, or isopropanol; water; a
mixture of hydrophilic organic solvents and water; certain
interparticle crosslinking agents as hereinbefore described;
volatile hydrophobic organic compounds such as hexane, octane,
benzene or toluene; or mixtures thereof. Preferred associating
agents are water, methanol, isopropanol, ethanol, interparticle
crosslinking agents such as glycerol, or mixtures thereof.
Typically the associating agent comprises a mixture including an
interparticle crosslinking agent such that the step of applying an
interparticle crosslinking agent is carried out simultaneously with
the step of applying an associating agent.
The associating agents may be applied to the precursor particles by
any of various techniques and apparatus used for applying solutions
to materials including coating, dumping, pouring, spraying,
atomizing, condensing, or immersing the associating agent on the
precursor particles. The associating agent is applied onto at least
a portion of the surface area of at least one of the precursor
particles to be joined per aggregate. Preferably, the associating
agent is coated onto the entire surface of most, preferably all, of
the precursor particles. The associating agent is generally mixed
with the precursor particles by any of a number of mixing
techniques and mixing apparatus to insure that the precursor
particles are thoroughly coated with the associating agent.
When an associating agent has been applied to the precursor
particles, the precursor particles may be physically contacted
together in a number of different ways. For example, the
associating agent alone may hold the particles together in contact.
Alternatively, gravitational forces may be used to insure contact
between the precursor particles. Further, the particles may be
placed in a container having a fixed volume so as to insure contact
between the precursor particles.
The precursor particles can alternatively be physically associated
together by physically constraining the precursor particles such
that they are in contact with each other. For example, the
precursor particles may be packed tightly into a container having a
fixed volume such that the precursor particles physically contact
each other. Alternatively or in combination with the above
procedure, gravitational forces may be used to physically associate
the precursor particles. The precursor particles may also be
physically associated together via electrostatic attraction or by
the introduction of an adhering agent (e.g., an adhesive material
such as a water-soluble adhesive) to adhere them together. The
precursor particles may also be attached to a third member (a
substrate) such that the precursor particles are brought into
contact with each other by the substrate.
In an alternative and preferred step in forming the macrostructures
of the present invention, the aggregate of the precursor particles
is shaped into various geometries, spatial relationships, and
densities to form an aggregate having a defined shape, size, and/or
density. The aggregate may be shaped by any conventional shaping
techniques as are known in the art. Preferred methods for shaping
the aggregate include casting, molding, or forming operations.
Casting and molding techniques generally involve introducing the
precursor particles into a prepared mold cavity and applying
pressure to (compressing) the aggregate to cause the aggregate to
conform to the shape of the mold cavity. Examples of specific
molding techniques for use herein include compression molding,
injection molding, extrusion or laminating. For example, a
multiplicity of precursor particles may be added to a container
having a fixed volume mold cavity and the aggregate compressed to
conform to the shape of the mold cavity so that the resultant
macrostructure has a shape defined by the shape of the mold cavity.
Forming techniques involve performing various operations on the
aggregate to modify its shape, and/or size, and/or density.
Examples of specific forming techniques for use herein include
rolling, forging, extruding, spinning, coating or drawing
operations. For example, an aggregate mixture of the precursor
particles and at least the interparticle crosslinking agent may by
passed between a pair of compaction rolls to form a sheet
aggregate. Alternatively, the aggregate mixture may by extruded
through an orifice to form an aggregate having a shape
corresponding to the shape of the orifice. Further, the aggregate
mixture may be cast on a surface to form an aggregate having a
desired shape or surface morphology. Any or all of these techniques
may also be used in combination to form the shaped aggregate. Any
suitable apparatus as are known in the art may be used to carry out
such operations, and the operation may be performed with the
material or portions of the apparatus either hot and/or cold.
In a preferred embodiment of the present invention, an aggregate
mixture of precursor particles, an interparticle crosslinking
agent, water, and a hydrophilic organic solvent are added to the
hopper of a conventional extruder apparatus. An example of an
extruder apparatus is shown in FIGS. 12-14 of Principles of Polymer
Materials, Second Edition (McGraw-Hill Book Company, 1982) at page
331, which publication is incorporated herein by reference. The
aggregate mixture is extruded through the orifice of the extruder
apparatus to feed a pair of driven compaction rolls having a fixed
(but variable) gap between the rolls so as to compress the
aggregate into the form of a sheet. The sheet is then processed to
specific lengths to provide macrostructures that have a
specifically designed size, shape, and/or density.
Simultaneously or after the interparticle crosslinking agent has
been applied, the precursor particles have been physically
associated together to form an aggregate, and the aggregate has
been shaped, the interparticle crosslinking agent is reacted with
the polymer material of the precursor particles of the aggregate,
while maintaining the physical association of the precursor
particles, to form crosslink bonds between the precursor particles
to form an interparticle crosslinked aggregate macrostructure.
The reaction between the interparticle crosslinking agent and the
polymer material must be activated and completed to form the
crosslink bonds between different precursor particles to form the
interparticle crosslinked aggregate. Although the crosslinking
reaction may be activated by irradiation (e.g., ultraviolet, gamma-
or X-radiation) or by a catalyst as an initiator and an activator,
the crosslinking reaction is preferably thermally activated
(heating). Heating activates and drives the reaction and drives off
any volatiles present in the mixture. Such reaction conditions will
generally involve heating the associated precursor particles and
the interparticle crosslinking agent for certain times and at
certain temperatures. The heating step can be carried out using a
number of different apparatus as are known including the various
ovens or driers as are known in the art.
Generally, the reaction is effected by heating to a temperature
above about 90.degree. C. for a sufficient time to complete the
crosslinking reaction. For each set of specific interparticle
crosslinking agent(s) and polymer material of the precursor
particles used, if the temperature is too low or the time is too
short, the reaction will not be sufficiently driven resulting in
fewer and weaker interparticle crosslink bonds thereby causing some
loss of liquid permeability of the macrostructure upon swelling. If
the temperature is too high, the absorbency of the precursor
particles may be degraded or the network crosslinks of these
precursor particles, depending upon the specific polymer materials,
may be degraded to such a point that the resultant macrostructure
is not useful for absorbing large quantities of liquids. In
addition, if the time and temperatures are not correct, the
extractable levels of the resultant aggregates may increase,
thereby increasing the incidence of that form of gel blocking.
Therefore, the reaction will generally be carried out at a
temperature in the range from about 120.degree. C. to about
300.degree. C., more preferably from about 100.degree. C. to about
250.degree. C. The time to complete the reaction, in the absence of
catalysts, will generally be from about 5 minutes to about 6 hours,
more preferably from about 10 minutes to about 4 hours.
For the preferred polymer material of the precursor particles,
slightly network crosslinked products of partially neutralized
polyacrylic acid, and the preferred interparticle crosslinking
agents, such as glycerol or trimethylol propane, such reaction
conditions will involve a temperature of from about 170.degree. C.
to about 220.degree. C. for about 3 hours to about 30 minutes,
respectively. More preferably, the reaction is carried out at a
temperature between about 190.degree. C. to about 210.degree. C.
for about 75 minutes to about 45 minutes, respectively. The actual
time and temperatures used will vary depending upon the specific
polymer materials used for the precursor particles, the specific
interparticle crosslinking agents used, the presence or absence of
a catalyst used to drive the reaction, and the thickness or
diameter of the macrostructure.
The crosslinking reaction can be promoted by adding an initiator
and/or a catalyst to the interparticle crosslinking agent to reduce
the time and/or the temperature and/or the amount of interparticle
crosslinking agent required to join the precursor particles
together. Generally, however, the reaction is conducted in the
absence of a catalyst.
The physical association of the precursor particles needs to be
maintained during the reaction step so that sufficient
interparticle crosslink bonds are formed. If forces or stresses
sufficient to dissociate the precursor particles are present during
the reaction step, the crosslink bonds between the precursor
particles (interparticle crosslink bonds) may not be formed. The
physical association of the precursor particles is typically
maintained by insuring minimal dissociation forces or stresses are
introduced during the reaction step.
As an optional and preferred step in the method of forming the
porous, absorbent, polymeric macrostructure, the component
precursor particles of the macrostructure are surface treated. For
example, U.S. Pat. No. 4,824,901 issued to Alexander et al. on Apr.
25, 1989, discloses the surface treatment of polymeric particles
with a poly-quaternary amine. In an exemplary method, the polymer
material existing at least in the vicinity of the surface of the
precursor particles is surface crosslinked such as disclosed in
U.S. Pat. No. 4,666,983, entitled "Absorbent Article" issued to
Tsubakimoto et al. on May 19, 1987; and U.S. Pat. No. 4,734,478,
entitled "Water Absorbing Agent" issued to Tsubakimoto et al. on
Mar. 29, 1988; which patents are incorporated herein by reference.
By utilizing a surface crosslinking step in the present invention,
the resistance to deformation of the resultant macrostructure, when
swollen, is improved. Preferably, the interparticle crosslinking
agent applied to the precursor particles also serves as the surface
crosslinking agent such that the macrostructure is preferably
simultaneously formed and surface crosslinked.
As previously discussed, the steps in the method for producing the
macrostructure need not be carried out in any specific order. In
addition, the steps may be carried out simultaneously.
In a preferred embodiment, the interparticle crosslinking agent is
applied simultaneously with the physical association of the
precursor particles, the mixture is subsequently shaped into a
preferred shape and typically a desired density, and the
interparticle crosslinking agent is subsequently reacted with the
polymer material of the precursor particles, either immediately
after the above steps are completed or after the aggregate has been
left standing for a period of time, to simultaneously form and
surface crosslink the macrostructure. Typically, the precursor
particles are introduced into a vessel and mixed with a solution of
an interparticle crosslinking agent, water, and a hydrophilic
organic solvent atomized onto the precursor particles to form an
aggregate. The interparticle crosslinking agent, water, and the
hydrophilic organic solvent serves as an associating agent for the
precursor particles. The interparticle crosslinking agent also
serves as a surface crosslinking agent. The aggregate (i.e., the
associated precursor particles and the aqueous mixture) are
subsequently shaped into a densified sheet-form by a combination of
extruding and rolling techniques as described above. The
interparticle crosslinking agent is subsequently reacted by heating
with the polymer material to form crosslink bonds between the
precursor particles to form an interparticle crosslinked aggregate
macrostructure and simultaneously to surface crosslink the surfaces
of the precursor particles of the resultant macrostructure.
Under certain conditions, the resultant macrostructures can be
somewhat inflexible and brittle. More flexible macrostructures can
be obtained in several ways. For example, a plasticizer can be
added to the macrostructure after the interparticle crosslinking
reaction is complete. Suitable plasticizers include water, high
molecular weight hydrophilic organic solvents (e.g., glycerol;
1,3-propanediol; or ethylene glycol), or polymeric solutions (e.g.,
polyvinyl alcohol or polyethylene glycol), or mixtures thereof. The
plasticizer can be applied to the macrostructures in a number of
different ways including spraying, coating, atomizing, immersing,
or dumping the solution onto the macrostructure. Alternatively, in
the case of water, the plasticizer may be added via placing the
macrostructure into a high humidity environment (e.g., greater than
70% relative humidity). A plasticizer may also be added to the
pre-reaction mixture containing a polymerizable monomer with the
monomer being subsequently reacted to form interparticle polymeric
crosslink bonds. In this case, the plasticizer is entrapped in the
interparticle crosslink bond structures during the crosslinking
reaction. The amount of plasticizer present in the solution is
selected depending upon the specific plasticizer being used.
Typically, the plasticizer comprises from about 0.01 parts to about
100 parts by weight of the plasticizer per 100 parts by weight of
the precursor particles.
As shown in FIGS. 1-3, the resultant macrostructure has pores (the
dark areas of the photomicrograph) between adjacent precursor
particles. The pores are small interstices between adjacent
precursor particles that allow the passage of liquid into the
interior of the macrostructure. The pores are formed into the
macrostructure because the precursor particles do not "fit" or pack
tightly enough, even when compressed, to eliminate the pores. (The
packing efficiency of the precursor particles is less than 1.) The
pores are generally smaller than the constituent precursor
particles and provide capillaries between the precursor particles
to transport liquid into the interior of the macrostructure.
The pores are interconnected with each other by intercommunicating
channels between the pores. The channels allow liquids contacting
the macrostructure to be transported via capillary forces (i.e.,
capillary channels are formed) to other portions of the
macrostructure so that the total volume of the macrostructure is
used in absorbing such liquids. Further, when swollen, the pores
and the intercommunicating channels allow liquids to pass through
the macrostructure either to layers of precursor particles remote
from the initial point of liquid contact or to other structures in
contact with the macrostructure. Thus, the macrostructure is
considered to be liquid permeable due to the pores and the
intercommunicating channels.
The void fraction (i.e., the total volume of the macrostructure
that comprises the pores and the channels) has a minimum value for
a given precursor particle size distribution. In general, the
narrower the precursor particle size distribution, the higher the
void fraction will be. Thus, it is preferred, so as to provide
higher void fractions in a densified state, that the precursor
particles have a relatively narrow particle size distribution.
Another feature of the macrostructures of the present invention is
that the macrostructures swell generally isotropically, even under
moderate confining pressures, when liquids are deposited onto or
come into contact with the macrostructures. Isotropic swelling is
used herein to mean that the macrostructure swells generally
equally in all directions when wetted. Isotropic swelling is an
important property of the macrostructure because the precursor
particles and the pores are able to maintain their relative
geometry and spatial relationships even when swollen such that the
existing capillary channels are maintained, if not enlarged, during
use. (The pores and the precursor particles get larger during
swelling.) Thus, the macrostructure can imbibe and/or transport
through itself additional loadings of liquid while not gel
blocking.
An indication that crosslink bonds are being formed in the
macrostructure between the previously independent precursor
particles is that the resultant macrostructures are fluid (i.e.,
liquid) stable. "Fluid stable" is used herein to mean a
macrostructure comprising an interparticle crosslinked aggregate
that upon contact with or swelling (with and/or without stress) in
an aqueous fluid remains substantially intact (i.e., most of the
previously independent component precursor particles remain joined
together). While the definition of fluid stability recognizes that
most of the precursor particles remain joined together, preferably
all of the precursor particles used to make up the macrostructure
remain joined together. However, it should be recognized that some
of the precursor particles may dissociate themselves from the
macrostructure if, for example, other particles have been
subsequently water agglomerated to the macrostructure.
Fluid stability is an important feature of the macrostructures of
the present invention because it allows the aggregate to maintain
its relative structure in both the dry and swollen states, and
because it immobilizes component precursor particles. In an end
product such as an absorbent member or an absorbent article, fluid
stability is beneficial in reducing gel blocking since precursor
particles remain aggregated even when contacted with liquid, and
allows one to use previously independent fine particles in an
aggregate form to increase the rate of fluid uptake of the
resultant macrostructure without introducing the element of gel
blocking.
Fluid stability can be measured in an aggregate macrostructure by a
two step process. The initial dynamic response of the aggregate
macrostructure upon contact with the aqueous fluid is observed and
then the fully swollen equilibrium condition of the aggregate
macrostructure is observed. A test method for determining fluid
stability based on these criteria is hereinafter described in the
Test Methods section.
In use, liquids that are deposited onto or come in contact with the
macrostructures are imbibed by the precursor particles or are
passed into the pores and transmitted to other portions of the
macrostructure where they are imbibed by other precursor particles
or transported through the macrostructure to other absorbent
members adjacent thereto.
FIGS. 4-6 show an alternative embodiment of the present invention
wherein the precursor particles comprise different shapes and
chemistries. The precursor particles consist of a mixture of
irregular-shaped granules and fibers (i.e., superabsorbent fibers).
In the embodiment shown in FIGS. 4-6, the fibers are FIBERSORB
fibers as available from the Arco Chemical Company of Wilmington,
Del. FIG. 4 shows the general shape of such a macrostructure. As
shown in FIG. 4, the fibers provide a matrix wherein relatively
small pores are formed between the granules and relatively large
pores are formed about the fibers. FIG. 5 shows more detail
relating to the shape and size of the pores and that the granules
are interparticle crosslinked to the fibers. FIG. 6 shows in more
detail the large pores and channels formed in the macrostructure by
the addition of the fibers and the particle/fiber bonding.
The relative amount of superabsorbent fibers mixed with the
granules can vary widely. For example, the macrostructure may be
formed of only the superabsorbent fibers; the resultant
macrostructure having the appearance of nonwoven fiber webs. In the
embodiments shown in FIGS. 4-6, the superabsorbent fibers comprise
from about 0.1% to about 50%, more preferably from about 0.5% to
about 10%, by weight of the total amount of precursor
particles.
When superabsorbent fibers comprise a portion of the precursor
particles, the fibers are preferably thoroughly mixed with the
other precursor particles so that the fibers are interwoven between
many different precursor particles.
FIG. 7 shows an alternative embodiment of a macrostructure of the
present invention wherein reinforcing members such as fibers
(fibrous or fiber material) are embedded in the macrostructure. The
reinforcing members provide strength (i.e., structural integrity)
to the swollen macrostructure. In certain embodiments, the
reinforcing fibers also provide members that quickly wick liquids
to other portions of the macrostructure and/or additional absorbent
material. The reinforcing members preferably comprise fibers (also
referred to as reinforcing fibers); although other materials such
as filaments, coils, webs, nonwoven webs, woven webs, or scrims as
are known for their reinforcing properites may be used. FIG. 7
shows an embodiment wherein polyester fibers are interwoven
throughout the macrostructure. Specifically, the polyester fibers
are contained within the intercommunicating channels to provide
increased swollen structural integrity for the macrostructure.
Various types of fiber material can be used for the reinforcing
members in the macrostructures of the present invention. Any type
of fiber material which is suitable for use in conventional
absorbent products is also suitable for use in the macrostructures
herein. Specific examples of such fiber material include cellulose
fibers, modified cellulose fibers, rayon, polypropylene, and
polyester fibers such as polyethylene terephthalate (DACRON),
hydrophilic nylon (HYDROFIL), and the like. Examples of other fiber
materials for use in the present invention in addition to some
already discussed are hydrophilized hydrophobic fibers, such as
surfactant-treated or silica-treated thermoplastic fibers derived,
for example, from polyolefins such as polyethylene or
polypropylene, polyacrylics, polyamides, polystyrenes,
polyurethanes and the like. In fact, hydrophilized hydrophobic
fibers which are in and of themselves not very absorbent and which,
therefore, do not provide webs of sufficient absorbent capacity to
be useful in conventional absorbent structures, are suitable for
use in the macrostructures of the present invention by virtue of
their good wicking properties. This is because, in the
macrostructures herein, the wicking propensity of the fibers is as
important, if not more important, than the absorbent capacity of
the fiber material itself due to the high rate of fluid uptake and
lack of gel blocking properties of the macrostructures of the
present invention. Synthetic fibers are generally preferred for use
herein as the fiber component of the macrostructure. Most preferred
are polyolefin fibers, preferably polyester fibers.
Other cellulosic fiber materials which may be useful in certain
macrostructures herein are chemically stiffened cellulosic fibers.
Preferred chemically stiffened cellulosic fibers are the stiffened,
twisted, curled cellulosic fibers which can be produced by
internally crosslinking cellulose fibers with a crosslinking agent.
Types of stiffened, twisted, curled cellulose fibers useful as the
hydrophilic fiber material herein are described in greater detail
in U.S. Pat. No. 4,888,093 entitled "Individualized, Crosslinked
Fibers And Process For Making Said Fibers" issued to Dean et al. on
Dec. 19, 1989; U.S. Pat. No. 4,889,595 entitled "Process For Making
Individualized, Crosslinked Fibers Having Reduced Residuals And
Fibers Thereof" issued to Herron et al. on Dec. 26, 1989; U.S. Pat.
No. 4,889,596 entitled "Process For Making Individualized
Crosslinked Fibers And Fibers Thereof" issued to Schoggen et al. on
Dec. 26, 1989; U.S. Pat. No. 4,889,597 entitled "Process For Making
Wet-Laid Structures Containing Individualized Stiffened Fibers"
issued to Bourbon et al. on Dec. 26, 1989; and U.S. Pat. No.
4,898,647 entitled "Twisted, Chemically Stiffened Fibers And
Absorbent Structures Made Therefrom" issued to Moore et al. on Feb.
6, 1990. Each of these patents are incorporated herein by
reference.
As used herein, the term "hydrophilic" describes fibers or the
surfaces of fibers which are wetted by the liquids deposited onto
the fibers (i.e., if water or aqueous body fluid readily spreads on
or over the surface of the fiber without regard to whether or not
the fiber actually imbibes fluid or forms a gel). The state of the
art respecting wetting of materials allows definition of
hydrophobicity (and wetting) in terms of contact angles and the
surface tension of the liquids and solids involved. This is
discussed in detail in the American Chemical Society Publication
entitled Contact Angle, Wettability, and Adhesion edited by Robert
F. Gould and copyrighted in 1964. A fiber or surface of a fiber is
said to be wetted by a liquid either when the contact angle between
the liquid and the fiber or surface is less than 90.degree. or when
the liquid will tend to spread spontaneously across the surface of
the fiber; both conditions normally coexisting.
The fiber material may be added to the macrostructures by
introducing the fibers into solution with the interparticle
crosslinking agent, by mixing with the precursor particles prior to
applying the interparticle crosslinking agent, or by adding the
fiber material to the interparticle crosslinking agent/precursor
particle mixture. In a preferred embodiment, the fiber material is
kneaded into the interparticle crosslinking agent/precursor
particle mixture. The fiber material is preferably thoroughly mixed
with the solutions so that the fiber material is uniformly
dispersed throughout the macrostructure. The fibers are also
preferably added before reacting the interparticle crosslinking
agent with the polymer material of the precursor particles.
The relative amount of fiber material mixed with the precursor
particles can vary widely. The fiber material is preferably added
in a range from about 0.01 parts to about 5 parts, more preferably
in the range of from about 0.5 parts to about 2 parts, by weight
per 100 parts by weight of the precursor particles.
The porous, absorbent, polymeric macrostructures can be used for
many purposes in many fields of use. For example, the
macrostructures can be used for packing containers; drug delivery
devices; wound cleaning devices; burn treatment devices; ion
exchange column materials; construction materials; agricultural or
horticultural materials such as seed sheets or water-retentive
materials; and industrial uses such as sludge or oil dewatering
agents, materials for the prevention of dew formation, dessicants,
and humidity control materials.
The porous, absorbent, polymeric macrostructures of the present
invention are useful when joined to a carrier. Carriers useful in
the present invention include absorbent materials such as cellulose
fibers. The carriers also may be any other carriers as are known in
the art such as nonwoven webs, tissue webs, foams, polyacrylate
fibers, apertured polymeric webs, synthetic fibers, metallic foils,
elastomers, and the like. The macrostructures may be joined
directly or indirectly to the carriers and may be joined thereto
via chemical or physical bonding such as are known including
adhesives or chemicals that react to adhere the macrostructures to
the carriers.
Because of the unique absorbent properties of the porous,
absorbent, polymeric macrostructures of the present invention, the
macrostructures are especially suitable for use as absorbent cores
in absorbent articles, especially disposable absorbent articles. As
used herein, the term "absorbent article" refers to articles which
absorb and contain body exudates and more specifically refers to
articles which are placed against or in proximity to the body of
the wearer to absorb and contain the various exudates discharged
from the body. Additionally, "disposable" absorbent articles are
those which are intended to be discarded after a single use (i.e.,
the original absorbent article in its whole is not intended to be
laundered or otherwise restored or reused as an absorbent article,
although certain materials or all of the absorbent article may be
recycled, reused, or composted). A preferred embodiment of a
disposable absorbent article, diaper 20, is shown in FIG. 8. As
used herein, the term "diaper" refers to a garment generally worn
by infants and incontinent persons that is worn about the lower
torso of the wearer. It should be understood, however, that the
present invention is also applicable to other absorbent articles
such as incontinent briefs, incontinent pads, training pants,
diaper inserts, sanitary napkins, facial tissues, paper towels, and
the like.
FIG. 8 is a perspective view of the diaper 20 of the present
invention in its uncontracted state (i.e., with all the elastic
induced contraction removed) with portions of the structure being
cut-away to more clearly show the construction of the diaper 20 and
with the portion of the diaper 20 which contacts the wearer facing
the viewer. The diaper 20 is shown in FIG. 8 to preferably comprise
a liquid pervious topsheet 38; a liquid impervious backsheet 40
joined with the topsheet 38; an absorbent core 42 positioned
between the topsheet 38 and the backsheet 40; elastic members 44;
and tape tab fasteners 46. While the topsheet 38, the backsheet 40,
the absorbent core 42, and the elastic members 44 may be assembled
in a variety of well known configurations, a preferred diaper
configuration is described generally in U.S. Pat. No. 3,860,003
entitled "Contractable Side Portions For Disposable Diaper", which
issued to Kenneth B. Buell on Jan. 14, 1975, and which patent is
incorporated herein by o reference. Alternatively preferred
configurations for disposable diapers herein are also disclosed in
U.S. Pat. No. 4,808,178 entitled "Disposable Absorbent Article
Having Elasticized Flaps Provided With Leakage Resistant Portions"
issued to Mohammed I. Aziz and Ted L. Blaney on Feb. 28, 1989; U.S.
Pat. No. 4,695,278 entitled =Absorbent Article Having Dual Cuffs"
issued to Michael I. Lawson on Sept. 22, 1987; and U.S. Pat. No.
4,816,025 entitled "Absorbent Article Having A Containment Pocket"
issued to John H. Foreman on Mar. 28, 1989. These patents are
incorporated herein by reference.
FIG. 8 shows a preferred embodiment of the diaper 20 in which the
topsheet 38 and the backsheet 40 are co-extensive and have length
and width dimensions generally larger than those of the absorbent
core 42. The topsheet 38 is joined with and superimposed on the
backsheet 40 thereby forming the periphery of the diaper 20. The
periphery defines the outer perimeter or the edges of the diaper
20. The periphery comprises the end edges 32 and the longitudinal
edges 30.
The topsheet 38 is compliant, soft feeling, and non-irritating to
the wearer's skin. Further, the topsheet 38 is liquid pervious
permitting liquids to readily penetrate through its thickness. A
suitable topsheet 38 may be manufactured from a wide range of
materials such as porous foams, reticulated foams, apertured
plastic films, natural fibers (e.g., wood or cotton fibers),
synthetic fibers (e.g., polyester or polypropylene fibers) or from
a combination of natural and synthetic fibers. Preferably, the
topsheet 38 is made of a hydrophobic material to isolate the
wearer's skin from liquids in the absorbent core 42.
A particularly preferred topsheet 38 comprises staple length
polypropylene fibers having a denier of about 1.5, such as Hercules
type 151 polypropylene marketed by Hercules, Inc. of Wilmington,
Del. As used herein, the term "staple length fibers" refers to
those fibers having a length of at least about 15.9 mm (0.62
inches).
There are a number of manufacturing techniques which may be used to
manufacture the topsheet 38. For example, the topsheet 38 may be
woven, nonwoven, spunbonded, carded, or the like. A preferred
topsheet is carded, and thermally bonded by means well known to
those skilled in the fabrics art. Preferably, the topsheet 38 has a
weight from about 18 to about 25 grams per square meter, a minimum
dry tensile strength of at least about 400 grams per centimeter in
the machine direction, and a wet tensile strength of at least about
55 grams per centimeter in the cross-machine direction.
The backsheet 40 is impervious to liquids and is preferably
manufactured from a thin plastic film, although other flexible
liquid impervious materials may also be used. The backsheet 40
prevents the exudates absorbed and contained in the absorbent core
42 from wetting articles which contact the diaper 20 such as
bedsheets and undergarments. Preferably, the backsheet 40 is
polyethylene film having a thickness from about 0.012 mm (0.5 mil)
to about 0.051 centimeters (2.0 mils), although other flexible,
liquid impervious materials may be used. As used herein, the term
"flexible" refers to materials which are compliant and which will
readily conform to the general shape and contours of the wearer's
body.
A suitable polyethylene film is manufactured by Monsanto Chemical
Corporation and marketed in the trade as Film No. 8020. The
backsheet 40 is preferably embossed and/or matte finished to
provide a more clothlike appearance. Further, the backsheet 40 may
permit vapors to escape from the absorbent core 42 while still
preventing exudates from passing through the backsheet 40.
The size of the backsheet 40 is dictated by the size of the
absorbent core 42 and the exact diaper design selected. In a
preferred embodiment, the backsheet 40 has a modified
hourglass-shape extending beyond the absorbent core 42 a minimum
distance of at least about 1.3 centimeters to about 2.5 centimeters
(about 0.5 to about 1.0 inch) around the entire diaper
periphery.
The topsheet 38 and the backsheet 40 are joined together in any
suitable manner. As used herein, the term "joined" encompasses
configurations whereby the topsheet 38 is directly joined to the
backsheet 40 by affixing the topsheet 38 directly to the backsheet
40, and configurations whereby the topsheet 38 is indirectly joined
to the backsheet 40 by affixing the topsheet 38 to intermediate
members which in turn are affixed to the backsheet 40. In a
preferred embodiment, the topsheet 38 and the backsheet 40 are
affixed directly to each other in the diaper periphery by
attachment means (not shown) such as an adhesive or any other
attachment means as known in the art. For example, a uniform
continuous layer of adhesive, a patterned layer of adhesive, or an
array of separate lines or spots of adhesive may be used to affix
the topsheet 38 to the backsheet 40.
Tape tab fasteners 46 are typically applied to the back waistband
region of the diaper 20 to provide a fastening means for holding
the diaper on the wearer. The tape tab fasteners 46 can be any of
those well known in the art, such as the fastening tape disclosed
in U.S. Pat. No. 3,848,594 issued to Kenneth B. Buell on Nov. 19,
1974, which patent is incorporated herein by reference. These tape
tab fasteners 46 or other diaper fastening means are typically
applied near the corners of the diaper 20.
The elastic members 44 are disposed adjacent the periphery of the
diaper 20, preferably along each longitudinal edge 30, so that the
elastic members 44 tend to draw and hold the diaper 20 against the
legs of the wearer. Alternatively, the elastic members 44 may be
disposed adjacent either or both of the end edges 32 of the diaper
20 to provide a waistband as well as or rather than leg cuffs. For
example, a suitable waistband is disclosed in U.S. Pat. No.
4,515,595 entitled "Disposable Diapers with Elastically
Contractible Waistbands" which issued to David J. Kievit and Thomas
F. Osterhage on May 7, 1985, which patent is herein incorporated by
reference. In addition, a method and apparatus suitable for
manufacturing a disposable diaper having elastically contractible
elastic members is described in U.S. Pat. No. 4,081,301 entitled
"Method and Apparatus for Continuously Attaching Discrete,
Stretched Elastic Strands to Predetermined Isolated Portions of
Disposable Absorbent Products" which issued to Kenneth B. Buell on
Mar. 28, 1978 and which patent is incorporated herein by
reference.
The elastic members 44 are secured to the diaper 20 in an
elastically contractible condition so that in a normally
unrestrained configuration, the elastic members 44 effectively
contract or gather the diaper 20. The elastic members 44 can be
secured in an elastically contractible condition in at least two
ways. For example, the elastic members 44 may be stretched and
secured while the diaper 20 is in an uncontracted condition.
Alternatively, the diaper 20 may be contracted, for example, by
pleating, and the elastic members 44 secured and connected to the
diaper 20 while the elastic members 44 are in their unrelaxed or
unstretched condition.
In the embodiment illustrated in FIG. 8, the elastic members 44
extend along a portion of the length of the diaper 20.
Alternatively, the elastic members 44 may extend the entire length
of the diaper 20, or any other length suitable to provide an
elastically contractible line. The length of the elastic members 44
is dictated by the diaper design.
The elastic members 44 may take a multitude of configurations. For
example, the width of the elastic members 44 may be varied from
about 0.25 millimeters (0.01 inches) to about 25 millimeters (1.0
inch) or more; the elastic members 44 may comprise a single strand
of elastic material or may comprise several parallel or
non-parallel strands of elastic material; or the elastic members 44
may be rectangular or curvilinear. Still further, the elastic
members 44 may be affixed to the diaper in any of several ways
which are known in the art. For example, the elastic members 44 may
be ultrasonically bonded, heat and pressure sealed into the diaper
20 using a variety of bonding patterns or the elastic members 44
may simply be glued to the diaper 20.
The absorbent core 42 of the diaper 20 is positioned between the
topsheet 38 and the backsheet 40. The absorbent core 42 may be
manufactured in a wide variety of sizes and shapes (e.g.,
rectangular, hourglass, asymmetrical, etc.) and from a wide variety
of materials. The total absorbent capacity of the absorbent core 42
should, however, be compatible with the design liquid loading for
the intended use of the absorbent article or diaper. Further, the
size and absorbent capacity of the absorbent core 42 may vary to
accommodate wearers ranging from infants through adults. The
absorbent core 42 comprises the porous, absorbent, polymeric
macrostructures of the present invention.
A preferred embodiment of the diaper 20 has a rectangular-shaped
absorbent core 42. As shown in FIG. 9, the absorbent core 42
preferably comprises an absorbent member 48 comprising an envelope
web 50 and a porous, absorbent, polymeric macrostructure 52
disposed in the envelope web 50. The macrostructure 52 is encased
in the envelope web 50 to minimize the potential for the precursor
particles to migrate through the topsheet and to provide an
additional liquid transport layer between the topsheet 38 and the
macrostructure 52 to enhance liquid acquisition and minimize rewet.
As shown in FIG. 9, a single envelope web 50 is wrapped about the
macrostructure 52 by folding to form a first layer 54 and a second
layer 56. The edges 58 of the envelope web 50 are sealed about its
periphery by any conventional means such as an adhesive 59 (as
shown), ultrasonic bonds, or heat/pressure bonds, to form a pouch
The envelope web 50 may comprise a number of materials including
nonwoven webs, paper webs, or webs of absorbent materials such as
tissue paper. The envelope web 50 preferably comprises a nonwoven
web similar to the webs used to form the topsheet 38. The nonwoven
web is preferably hydrophilic to allow liquids to rapidly pass
through the envelope web 50. Similar layered absorbent members
(laminates) are more fully described in U.S. Pat. No. 4,578,068
entitled "Absorbent Laminate Structure" issued to Timothy A.
Kramer, Gerald A. Young and Ronald W. Kock on Mar. 25, 1986, which
patent is incorporated herein by reference.
Alternatively, the absorbent cores 42 of the present invention may
consist solely of one or more (a multiplicity of the) porous,
absorbent, polymeric macrostructures of the present invention; may
comprise a combination of layers including the macrostructures of
the present invention; or any other absorbent core configurations
including one or more of the macrostructures of the present
invention.
FIG. 10 shows an alternative embodiment of the diaper 120
comprising a dual-layer absorbent core 142 comprising a modified
hourglass-shaped absorbent member 60 and a sheet 62 of the porous,
absorbent, polymeric macrostructure positioned subjacent the
absorbent member 60 (i.e., between the absorbent member 60 and the
backsheet 40).
The absorbent member 60 serves to quickly collect and temporarily
hold discharged liquids and to transport such liquids by wicking
from the point of initial contact to other parts of the absorbent
member 60 and to the macrostructure sheet 62. The absorbent member
60 preferably comprises a web or batt of fiber materials. Various
types of fiber material can be used in the absorbent member 60 such
as the fiber materials previously discussed herein. Cellulosic
fibers are generally preferred for use herein, wood pulp fibers
being especially preferred. The absorbent member 60 can also
contain specific amounts of a particulate, absorbent, polymeric
composition. The absorbent member 60, for example, can contain up
to about 50% by its weight of the polymeric composition. In the
most preferred embodiments, the absorbent member 60 contains from
0% to about 8% by its weight of a particulate, absorbent, polymeric
composition. In alternatively preferred embodiments, the absorbent
member 60 comprises chemically stiffened cellulosic fibers as
previously discussed herein. Exemplary embodiments of the absorbent
member 60 useful in the present invention are described in U.S.
Pat. No. 4,673,402 entitled "Absorbent Article With Dual-Layered
Cores" which issued to Paul T. Weisman, Dawn I. Houghton, and Dale
A. Gellert on June 16, 1987; and U.S. Pat. No. 4,834,735 entitled
"High Density Absorbent Members Having Lower Density and Lower
Basis Weight Acquisition Zones" issued to Miguel Alemany and
Charles J. Berg on May 30, 1989. These patents are hereby
incorporated herein by reference. Absorbent members having a
storage zone and an acquisition zone having a lower average density
and a lower average basis weight per unit area than the storage
zone so that the acquisition zone may effectively and efficiently
rapidly acquire discharged liquid are especially preferred for use
herein.
The absorbent member 60 can be of any desired shape, for example,
rectangular, oval, oblong, asymmetric or hourglass-shaped. The
shape of the absorbent member 60 may define the general shape of
the resulting diaper 120. In the preferred embodiments as shown in
FIG. 10, the absorbent member 60 is hourglass-shaped.
The macrostructure sheet 62 of the present invention need not be
the same size as the absorbent member 60 and can, in fact, have a
top surface which is substantially smaller or larger than the top
surface area of the absorbent member 60. As shown in FIG. 10, the
macrostructure sheet 62 is smaller than the absorbent member 60 and
has a top surface area from about 0.10 to about 1.0 times that of
the absorbent member 60. Most preferably, the top surface area of
the macrostructure sheet 62 will be only from about 0.10 to about
0.75, and most preferably from about 0.10 to about 0.5 times that
of the absorbent member 60. In an alternative embodiment, the
absorbent member 60 is smaller than the macrostructure sheet 62 and
has a top surface area from about 0.25 to about 1.0 times, more
preferably from about 0.3 to about 0.95 times that of the
macrostructure sheet 62. In this alternative embodiment, the
absorbent member 60 preferably comprises chemically stiffened
cellulosic fibers.
The macrostructure sheet 62 is preferably placed in a specific
positional relationship with respect to the backsheet 40 and/or the
absorbent member 60 in the diaper. More particularly, the
macrostructure sheet 62 is positioned generally toward the front of
the diaper so that the macrostructure sheet 62 is most effectively
located to acquire and hold discharged liquids.
In alternatively preferred embodiments, a multiplicity of
macrostructures, preferably from about two to about six
macrostructure strips or sheets, may be substituted for the single
macrostructure sheet 62 shown in FIG. 10. Further, additional
absorbent layers, members, or structures may be placed into the
absorbent core 142. For example, an additional absorbent member may
be positioned between the macrostructure sheet 62 and the backsheet
40 to provide reserve capacity for the absorbent core 142 and/or a
layer to distribute liquids passing through the macrostructure
sheet 62 to other portions of the absorbent core 142 or to the
macrostructure sheet 62. The macrostructure sheet 62 may also
alternatively be positioned over the absorbent member 60 so as to
be positioned between the topsheet 38 and the absorbent member
60.
In use, the diaper 20 is applied to a wearer by positioning the
back waistband region under the wearer's back, and drawing the
reminder of the diaper 20 between the wearer's legs so that the
front waistband region is positioned across the front of the
wearer. The tape-tab fasteners 46 are then secured preferably to
outwardly facing areas of the diaper 20. In use, disposable diapers
or other absorbent articles incorporating the porous, absorbent,
polymeric macrostructures of the present invention tend to more
quickly and efficiently distribute and store liquids and to remain
dry due to the high absorbent capacity of the macrostructures.
SYNTHETIC URINE
The specific synthetic urine used in the test methods of the
present invention is referred to herein as "Synthetic Urine". The
Synthetic Urine is commonly known as Jayco SynUrine and is
available from Jayco Pharmaceuticals Company of Camp Hill, Pa. The
formula for the Synthetic Urine is: 2.0 g/l of KCl; 2.0 g/l of
Na.sub.2 SO.sub.4 ; 0.85 g/l of (NH.sub.4)H.sub.2 PO.sub.4 ; 0.15
g/l (NH.sub.4).sub.2 HPO.sub.4 ; 0.19 g/l of CaCl.sub.2 and 0.23
g/l of MgCl.sub.2. All of the chemicals are of reagent grade. The
pH of the Synthetic Urine is in the range of 6.0 to 6.4.
TEST METHODS
A. Absorptive Capacity of the Precursor Particles
The polymeric composition is placed within a "tea bag", immersed in
an excess of Synthetic Urine for a specified period of time, and
then centrifuged for a specific period of time. The ratio of
polymeric composition final weight after centrifuging minus initial
weight (net fluid gain) to initial weight determines the Absorptive
Capacity.
The following procedure is conducted under standard laboratory
conditions at 23.degree. C. (73.degree. F.) and 50% relative
humidity. Using a 6 cm.times.12 cm cutting die, the tea bag
material is cut, folded in half lengthwise and sealed along two
sides with a T-bar sealer to produce a 6 cm.times.6 cm tea bag
square. The tea bag material utilized is a grade 1234 heat sealable
material, obtainable from C. H. Dexter, Division of the Dexter
Corp., Windsor Locks, Conn., U.S.A., or equivalent. Lower porosity
tea bag material should be used if required to retain fine
particles. 0.200 grams plus or minus 0.005 grams of the polymeric
composition is weighed onto a weighing paper and transferred into
the tea bag, and the top (open end) of the tea bag is sealed. An
empty tea bag is sealed at the top and is used as a blank.
Approximately 300 milliliters of Synthetic Urine are poured into a
1,000 milliliter beaker. The blank tea bag is submerged in the
Synthetic Urine. The tea bag containing the polymeric composition
(the sample tea bag) is held horizontally to distribute the
material evenly throughout the tea bag. The tea bag is laid on the
surface of the Synthetic Urine The tea bag is allowed to wet, for a
period of no more than one minute, and then is fully submerged and
soaked for 60 minutes. Approximately 2 minutes after the first
sample is submerged, a second set of tea bags, prepared identically
to the first set of blank and sample tea bags, is submerged and
soaked for 60 minutes in the same manner as the first set. After
the prescribed soak time is elapsed, for each set of tea bag
samples, the tea bags are promptly removed (using tongs) from the
Synthetic Urine. The samples are then centrifuged as described
below. The centrifuge used is a Delux Dynac II Centrifuge, Fisher
Model No. 05-100-26, obtainable from Fisher Scientific Co. of
Pittsburgh, Pa., or equivalent. The centrifuge should be equipped
with a direct read tachometer and an electric brake. The centrifuge
is further equipped with a cylindrical insert basket having an
approximately 2.5 inch (6.35 cm) high outer wall with an 8.435 inch
(21.425 cm) outer diameter, a 7.935 inch (20.155 cm) inside
diameter, and 9 rows each of approximately 106 3/32 inch (0.238 cm)
diameter circular holes equally spaced around the circumference of
the outer wall, and having a basket floor with six 1/4 inch (0.635)
cm) diameter circular drainage holes equally spaced around the
circumference of the basket floor at a distance of 1/2 inch (1.27
cm) from the interior surface of the outer wall to the center of
the drainage holes, or an equivalent. The basket is mounted in the
centrifuge so as to rotate, as well as brake, in unison with the
centrifuge. The sample tea bags are positioned in the centrifuge
basket with a folded end of the tea bag in the direction of the
centrifuge spin to absorb the initial force. The blank tea bags are
placed to either side of the corresponding sample tea bags. The
sample tea bag of the second set must be placed opposite the sample
tea bag of the first set; and the blank tea bag of the second set
opposite the blank tea bag of the first set, to balance the
centrifuge. The centrifuge is started and allowed to ramp up
quickly to a stable speed of 1,500 rpm. Once the centrifuge has
been stabilized at 1,500 rpm, a timer is set for 3 minutes. After 3
minutes, the centrifuge is turned off and the brake is applied. The
first sample tea bag and the first blank tea bag are removed and
weighed separately. The procedure is repeated for the second sample
tea bag and the second blank tea bag. The Absorptive Capacity (ac)
for each of the samples is calculated as follows: ac=(sample tea
bag weight after centrifuge minus blank tea bag weight after
centrifuge minus dry polymeric composition weight) divided by (dry
polymeric composition weight). The Absorptive Capacity value for
use herein is the average Absorptive Capacity of the two
samples.
B. Fluid Stability
The objective of this method is to determine the stability of an
aggregate upon exposure to Synthetic Urine.
The sample macrostructure is placed in a shallow dish. An excess
amount of Synthetic Urine is added to the macrostructure. The
swelling of the macrostructure is observed until equilibrium is
reached. During the observation of the swelling macrostructure, the
macrostructure is observed for small particles breaking off from
the main aggregate, platelet-like particles floating away from the
main aggregate, or particle expansion only in the two dimensional
x-y plane with particles breaking and floating away from the main
aggregate. If the aggregate has a large number of broken away
component particles, the macrostructure is considered unstable. The
macrostructure should also be observed for isotropic swelling. If
the aggregate remains relatively stable and the relative geometry
and spatial relationships of the precursor particles and the pores
are maintained after the test procedure, the macrostructure is
considered stable. Preferably, fluid stable macrostructures are
capable of being picked up in their swollen state without breaking
apart.
C. Precursor Particle Size and Mass Average Particle Size
The particle size distribution on a weight percent basis of a 10
gram bulk sample of the precursor particles is determined by
sieving the sample through a set of 19 sieves ranging in size from
a standard #20 sieve (850 microns) through a standard #400 sieve
(38 microns). The sieves are standard sieves as obtainable from the
Gilson Company, Inc. of Worthington, Ohio. The procedure is carried
out on three stacks of sieves at a time since the equipment used
cannot hold all 19 sieves at one time. A first stack contains
sieves #20, 25, 30, 35, 40, 45, and 50 plus the sieve pan; the
second stack contains sieves #60, 70, 80, 100, 120, and 140 plus
the sieve pan; the third stack contains sieves # 170, 200, 230,
270, 325, and 400 plus the sieve pan. The precursor particles
remaining on each of these sieves are then weighed to determine the
particle size distribution on a weight percent basis.
The first stack of sieves is mounted on a shaker and 10.0 grams
plus or minus 0.00 grams of the sample is placed on the #20 sieve.
The shaker used is a Vibratory 3-inch Sieve Shaker Model SS-5 as
obtainable from the Gilson Company, Inc. of Worthington, Ohio. The
stack is shaken for 3 minutes at approximately 2100 vibrations per
minute ("6" on the instrument dial). The sieve pan is then removed
and the stack set aside for later weighing. Using a soft brush, the
sample remaining on the sieve pan is transferred onto a weighing
paper. The second stack of sieves is mounted on the shaker and the
sample on the weighing paper is transferred onto the #60 sieve. The
second stack is shaken for 3 minutes at approximately 2100
vibrations per minute, the sample remaining on the sieve pan being
transferred to a weighing paper and the stack set aside. The third
stack of sieves is mounted on the shaker and the sample on the
weighing paper is transferred onto the #170 sieve. The third stack
is shaken for 3 minutes at approximately 2100 vibrations per
minute. A soft brush is used to transfer the contents of each given
sieve onto a tared weighing paper. The sample is weighed on a
standard three place scale and the weight of the sample on the
specific sieve is recorded. This step is repeated, using a fresh
weighing paper for each sample, for each sieve, and for the sample
remaining on the sieve pan after the third stack of sieves has been
shaken. The method is repeated for two additional 10 gram samples.
The average of the weights of the three samples for each sieve
determine the average particle size distribution on a weight
percent basis for each sieve size.
The Mass Average Particle Size of the 10 gram bulk sample is
calculated as follows: ##EQU1## wherein maps is the mass average
particle size; Mi is the weight of the particles on the specific
sieve; and D.sub.i is the "size parameter" for the specific sieve.
The size parameter, D.sub.i of a sieve is defined to mean the size
(in microns) of the next highest sieve. For example, a standard #50
sieve has a size parameter of 355 microns, which corresponds to the
size of the openings in a standard #45 sieve (the next highest
sieve). The Mass Average Particle Size for use herein is the
average of the mass average particle size of the three samples.
PRECURSOR PARTICLE EXAMPLE
A jacketed 10 liter twin arm stainless steel kneader measuring 220
mm.times.240 mm in the opening and 240 mm in depth, and having two
Sigma type blades possessing a rotational diameter of 120 mm is
sealed with a lid. An aqueous monomer solution is prepared
consisting of 37 weight % monomer. The monomer consists of 75 mole
% sodium acrylate and 25 mole % acrylic acid. 5500 grams of the
aqueous monomer solution is charged to the kneader vessel, which is
subsequently purged with nitrogen gas to remove the remaining
entrapped air. Then, the two Sigma type blades are set rotating at
rates of 46 rpm and the jacket is heated by the passage of
35.degree. C. water. 2.8 g of sodium persulfate and 0.14 g of
L-ascorbic acid are added as polymerization initiators.
Polymerization begins about four minutes after the addition of the
initiators. A peak temperature of 82.degree. C. is reached inside
the reaction system 15 minutes after the addition of the
initiators. The hydrated gel polymer is divided into particles
about 5 mm in size as the stirring is continued. The lid is removed
from the kneader 60 minutes after the start of the polymerization
and the material is removed from the kneader.
The resultant hydrated aqueous gel polymer thus obtained is spread
on a standard #50 size metal gauze and dried with hot air at
150.degree. C. for 90 minutes. The dried particles are pulverized
with a hammer type crusher and sifted with a standard #20 sieve
(850 microns) to obtain particles that pass through the standard
#20 sieve. The mass average particle size of these particles is 405
microns.
EXAMPLE 1
350.0 grams of precursor particles made in accordance with the
Precursor Particle Example are placed into a 5 quart standing
kitchen-type mixer. The precursor particles have a particle size
such that the precursor particles pass through a standard #60 sieve
(250 microns) and are retained on a standard #100 sieve (150
microns). A solution is prepared consisting of 7.0 grams of
glycerol, 35.0 grams of methanol, and 7.0 grams of water. This
solution is applied to the precursor particles by spraying the
solution onto the precursor particles with a Preval Sprayer
available from The Precision Valve Corporation of Yonkers, N.Y. The
solution is sprayed onto the precursor particles while the mixer is
operating. For the first fifteen seconds of spraying, the mixer is
run on its lowest speed setting. After the first fifteen seconds,
the mixer is run on its highest setting. The total spraying
operation requires 3 minutes of elapsed time to spray the entire
volume of the solution onto the precursor particles. The mixture is
mixed for an additional two minutes at the highest speed setting of
the mixer so that all of the precursor particles are thoroughly
wetted by the solution. The resultant mixture is then placed into
the hopper of an extrusion/compaction unit such as previously
described. The extruder screw has a length of 8 inches (20.3 cm)
and contains 5 flights, each flight being 1.5 inches (3.8 cm) in
length. The outside diameter of the extruder screw is 1.75 inches
(4.45 cm) and the screw-to-housing clearance is 0.20 inches (0.51
cm). The unit is activated such that the extruder screw turns at a
rate of 47 rpm. The mixture is extruded between two coated steel
compaction rolls (nip rolls) with a fixed (but variable) gap. The
compaction rolls have a diameter of 8.975 inches (22.8 cm) and are
driven at a rate of 5.4 rpm. The gap between the compaction rolls
is 0.015 inches (0.38 mm). The formed aggregate sheets are then
separated into approximately 12 to 15 inch (30 to 40 cm) lengths.
The resultant aggregate sheets are heated in a forced air
convection oven at 210.degree. C. for 45 minutes to react the
glycerol with the polymer material of the precursor particles. The
resultant sheets have a thickness (caliper) of about 0.031 inches
(0.8 mm) and a width of about 1.95 inches (4.95 cm).
EXAMPLE 2
A solution is prepared consisting of 0.5 grams of glycerol, 0.5
grams of water, and 3.0 grams of isopropanol. This solution is
applied to 25 grams of precursor particles made in accordance with
the Precursor Particle Example. The precursor particles have a
particle size such that the precursor particles pass through a
standard #40 sieve (425 microns) and are retained on a standard #50
sieve (300 microns). The mixture is thoroughly mixed with a
stirring spatula until all of the precursor particles are coated
with the above solution. The mixture is separated into
approximately equal portions. One half of the mixture is spread
evenly on a SUPERSTONE baking stone as is available from Sassafras
Enterprises Inc. of Evanston, Ill. The mixture is lightly
compressed on the stone. 0.16 grams of KODEL polyester fibers are
spread evenly onto the formed mixture. The polyester fibers are
1.25 inch (3.2 cm) staple cut length, crimped, 15.0 denier fibers.
The second half of the initial mixture is spread evenly on top of
the fibers and lightly compressed. This entire structure is then
rolled with a wooden rolling pin to a thickness of about 0.06
inches (1.5 mm). A sheet of MYLAR is placed on top of the sheet for
rolling in order to prevent the mixture from adhering to the
rolling pin. The edges of the sheet are then folded in on
themselves and the rolling process is repeated. This
folding/rolling (kneading) procedure is performed twice. The sheet
is then heated in a forced air circulating oven at 200.degree. C.
for 45 minutes to react the glycerol with the polymer material of
the precursor particles. The resultant macrostructure has a
thickness (caliper) of about 0.06 inches (1.5 mm).
EXAMPLE 3
A solution is prepared consisting of 1.6 grams of glycerol, 3.2
grams of water, and 12.8 grams of isopropanol. This solution is
applied to 80 grams of the precursor particles made in accordance
with the Precursor Particle Example. The precursor particles have a
particle size distribution such that 8% by weight pass through a
standard #20 sieve (850 microns) and are retained on a standard #30
sieve (600 microns); 15% by weight pass through a standard #30
sieve (600 microns) and are retained on a standard #40 sieve (425
microns); 22% by weight pass through a standard #40 sieve (425
microns) and are retained on a standard #50 sieve (300 microns);
36% by weight pass through a standard #50 sieve (300 microns) and
are retained on a standard #100 sieve (150 microns); and 19% by
weight pass through a standard # 100 sieve (150 microns). This
solution is thoroughly mixed using a stirring spatula until all of
the precursor particles are coated with the above solution. The
resultant mixture is then spread loosely on a SUPERSTONE baking
stone and rolled into a sheet having a thickness of about 0.06
inches (1.5 mm) using a wooden rolling pin. A sheet of MYLAR is
placed on top of the sheet for rolling in order to prevent the
mixture from adhering to the rolling pin. The sheet is then heated
at 200.degree. C. for 45 minutes in a forced air circulating oven
to react the glycerol with the polymer material of the precursor
particles. The resultant macrostructure has a thickness (caliper)
of about 0.06 inches (1.5 mm).
EXAMPLE 4
A solution is prepared consisting of 0.342 grams of glycerol, 0.136
grams of water, and 1.713 grams of methanol. Separately, 0.512
grams of FIBERSORB fibers available from the Arco Chemical Company
and 13.364 grams of precursor particles of a size such that all of
the particles pass through a standard #100 sieve (150 microns) and
made in accordance with the Precursor Particle Example are mixed
together to form a precursor particle mixture. The fibers are hand
cut from a tow and range in length from about 0.5 inches (1.25 cm)
to about 2.5 inches (6.35 cm). The above solution is added to the
precursor particle mixture and thoroughly mixed together with a
stirring spatula to form an aggregate mixture. The resultant
aggregate mixture is spread out on a six inch (15 cm) PYREX culture
dish and compressed with a small spatula to a thickness of about
0.15 inches (3.8 mm). The sheet is then heated at 200.degree. C.
for 40 minutes in a forced air circulating oven to react the
glycerol with the polymer material of the precursor particles (both
the polymers of the FIBERSORB and the particles made in the
Precursor Particle Example). The resultant macrostructure has a
particulate structure of a combination of relatively small
irregular shaped granules and fibers intermixed with the
granules.
EXAMPLE 5
A solution is prepared consisting of 0.023 grams of glycerol, 0.014
grams of water, and 0.580 grams of methanol. This solution is added
to 0.880 grams of precursor particles consisting of FIBERSORB
fibers as available from the Arco Chemical Company. The fibers are
hand cut from a tow and range in length from about 0.5 inches (1.25
cm) to about 2.5 inches (6.35 cm). The solution and the precursor
particles are thoroughly mixed together with a stirring spatula to
form an aggregate mixture. The resultant aggregate mixture is
spread out on a six inch (15 cm) PYREX culture dish and compressed
with a small spatula to a thickness of about 0.007 inches (0.178
mm). The sheet is then heated at 200.degree. C. for 30 minutes in a
forced air circulating oven to react the glycerol with the polymer
material of the precursor particles. The resultant macrostructure
comprises an interfiber crosslinked aggregate having a structure
similar to a nonwoven web.
While particular embodiments of the present invention have been
illustrated and described, it would be obvious to those skilled in
the art that various other changes and modifications can be made
without departing from the spirit and scope of the invention. It is
therefore intended to cover in the appended claims all such changes
and modifications that are within the scope of this invention.
* * * * *